- Створено: 26-09-21
- Останній вхід: 26-09-21
Опис: The best gaming chairs in 2021 The best gaming chair is the perfect finishing touch to a modern PC gaming setup. It really will bring your whole desktop together and make it look supremely suave. Yet these gaming thrones are good for more than style points, the top gaming chairs will also give your weary back an ample place to rest. This also explains why they can be so costly—keeping you in one piece isn't a cheap endeavour. If you've spent thousands of dollars on an extreme gaming PC build, it's only fair to give your gaming chair just as much attention. If you're simply looking for everyday comfort, the best gaming seats may seem over the top. With wannabe-racer bucket seats, and gaming chairs covered in satanic runes running rampant, we've made sure to include a few sleek office-style chairs in here too. Whichever route you go down, keep your posture in mind. Posture may be the last thing you think about when embarking on a ten-hour raid, but we implore you: Don't disregard ergonomics. We've tested tens of ergonomic gaming chair from today's most well-known companies to find luxurious and affordable places to park your rear. Check those out below. And if the chairs are a bit rich for your butt, then our cheap gaming chair roundup may be more up your street. The Secretlab Titan Evo 2022 is everything we've been looking for in a gaming chair. That's why it's rightfully taken the top spot in our best gaming chair guide from the previous incumbent, the Secretlab Titan. It was an easy decision to make, though. The Secretlab Titan Evo 2022 does everything the Titan, and Omega below, can, except better User-friendly ergonomics make the Titan Evo 2022 a great fit for long nights gaming or eight hours tapping away for work, and that comes down to its superb built-in back support. It's highly adjustable, which means you can nail down a great fit with ease. There's also something to be said for the 4D armrests, comfortable seat rest, and magnetic head cushion. You read that right, a magnetic head cushion. A simple solution to fiddly straps, the Titan Evo 2022 does away with all that with a couple of powerful magnets. Secretlab also reckons its new Neo Hybrid Leatherette material is more durable than ever, though there's still the option for the Softweave fabric we've raved about in the past. The chair is available in three sizes: S, R, and XL. As a complete package, then, the Secretlab Titan Evo 2022 is the archetype of a great gaming chair. It is a little pricier than its predecessors, but we think it's worth the price tag. And anyways, that higher price tag is why we still recommend the Omega below for a cheaper option while stock lasts. The Secretlab Omega is one of the most finely constructed chairs we've tested, and although it has largely been replaced by the Titan Evo 2022 above nowadays, the higher price tag of that chair might see the Omega remain a popular option for those looking to save a little cash. From the casters to the base, the lift mechanism, armrests, and seat back, Secretlab has used some of the best materials available. The Omega was upgraded with Secretlab's 2020 series of improvements, which includes premium metal in the armrest mechanism, making it silky smooth to adjust and even more durable, and adding the company's ridiculously durable PU Leather 2.0. The chair features a high-quality, cold-cured foam to provide support. It feels a little firm at first but gets more comfortable after extended use. The Omega stands out from the crowd with its velour memory foam lumbar and head pillows. These are so comfortable that we could smoothly fully recline the chair and take a nap if we wanted to. Though that's not a great look in the office... If you're looking to treat your body with a chair that will genuinely last, the Secretlab Omega is worth every penny. Perhaps you've heard of the Herman Miller Embody. It occupied a top position in our best office chair roundup for a long time, but that has come to an end. Not for lack of comfort or acclaim, simply because the famed chair manufacturer has partnered up with Logitech to create something tailor-made to our gaming rumps. Admittedly, the Logitech G x Herman Miller Embody doesn't differ much from its commercial cousin. That's hardly a mark against it, however. The Embody's cascading back support design and absurdly high quality make a welcome return but now comes with a few more flourishes to win over gamers. Specifically, extra cooling material designed to support a more active gaming position. It's not so much the changes that make the Embody stand out as one of the best gaming chair with footrest going. It's what's been kept the same. The tried and tested Embody design is simply one of the best chairs for office work or gaming. It's incredibly comfortable over prolonged use, supports an active and healthy posture, and is easily fitted to your frame. The warranty, too, is a standout feature. At 12 years, including labor, and rated to 24-hour use over that time, it's a chair that is guaranteed to last you over a decade, if not longer. So while the initial price tag may seem steep, and that it is, the reality is you're certain to get your money's worth in the long run. And your back will be thankful for it, too. If you're the sort of person who prioritizes functionality over flash, the NeueChair is an excellent option. This isn't to say it's not stylish—quite the opposite; the NeueChair comes in a sleek, muted obsidian or flashy chrome/silver, both with bold, sweet curved supports on the back and an attractive black mesh. But, more importantly, the NeueChair is built to last, with a heavy, sturdy industrial construction. Even the chair's weight in the packaging indicates a solid piece of carefully constructed industrial art: it's heavy and substantial. Assembling it is a breeze, as it comes in two discrete pieces and is simply a matter of inserting the casters and then pushing the two parts together. Almost every aspect of the seat is adjustable, from the armrests to the lumbar support system that lets you change the height depth of the backrest. It's one of the best office chairs I've ever had the pleasure to sit in, and if you can afford the admittedly steep price tag, well worth the investment. If you're a big and tall gamer, you might have noticed that there aren't many racing gaming chair that can support your unique build. Whether it's a lower weight capacity or too short, or even feels like it'll break as soon as you sit in it, finding a chair for you might seem nearly impossible. The AndaSeat Kaiser 2 screams large and in charge, supporting gamers up to 397lbs and 7ft tall. The Kaiser 2 is built on a solid steel frame with oversized bars to provide support. Covered in premium PVC leather and extra thick memory foam cushioning, the Kaiser 2 manages to look more like a gaming chair for grownups. Available in black and a lovely maroon, no more will have to stuff yourself into a tiny gaming chair hope for the best. The Kaiser 2 manages to do both the function, comfort, and style you want in your premium gaming chair. When buying a gaming chair, it's easy to forget your health. After all, most are advertised as luxurious, cushioned thrones that soothe your every ache as you smash the crap out of your foes in Apex Legends. But that isn't true, and for some, it's important to pick a chair that takes back support seriously. With some of the team have used it daily for almost a year, we can thoroughly recommend the Noblechairs Hero in uPVC leather. While not the most exciting of chairs, or the sportiest, it certainly does a good job of taking care of your back. The Hero is easy to assemble, except for the bit where you attach the back to the seat, so make sure you have a buddy for that. It's firm and supportive, and extremely sturdy. As a word of warning: it is substantial, so if you prefer a softer chair that isn't as good for your lumbar, this maybe isn't for you. Aside from that, it has a decent recline, can withstand frames of up to 330 lbs, and has fully adjustable wrist-rests. It's heavy but glides pretty easily on the supplied casters. It'll look just fine in both an office or gaming setup, so you're getting a chair that can do both. Not bad, if you can afford it. Corsair's latest addition to its lineup of premium reclining gaming chair, the T3 Rush, has gotten a much-needed facelift. The T3 Rush is an insanely comfy chair thanks to its memory foam lumbar pillow but, more importantly, uses a breathable soft fabric in place of faux leather. The benefit of this is that it retains less heat, keeping you fresh and comfy instead of sweating in your squeaky pleather. The Rush also reclines to a ridiculous 180 degrees in case you wanted to lie back and take a comfy cat nap before you take on another marathon streaming session of Apex Legends or CS: GO. The only major downside for the T3 Rush mostly fits for smaller framed users. If you require a little larger seat, the T3 will be an uncomfortably tight fit. Other than that, the T3 Rush is an impressive-looking gaming chair that doesn't need a loud color to make a statement. The DXRacer Master is a chair for people with money to spend, but it justifies the price by being an extremely luxuriant and comfortable chair. What's more, the DXRacer Master can be customized with modular parts (sold at an added cost) like mesh seat and backrests, leg rests, and even a rotating arm that bolts onto the base and can hold anything from a laptop to your phone. Choosing not to invest in these extra parts won't compromise the chair itself, though, because DXRacer went all out on its features. Built-in lumbar support and an adjustable, rail-mounted headrest are great features, along with four-dimensional armrests. The microfiber leather is especially nice, and much of the chair is made of metal, which makes it feel sturdy. It's clear that the DXRacer Master was built to last, and its understated look is great if you're not into the flashy designs seen on most other gaming chairs. But, boy, it will cost you for all this luxury: The DXRacer Master is still $80 more than the Secret Lab Omega, our favorite chair. But it's worth considering if you want to go all out and get something with all the bells and whistles.
Дата публікації: 26-09-21
Опис: Useful information on External Gear Pumps A gear pump is a type of positive displacement (PD) pump. Gear pumps use the actions of rotating cogs or gears to transfer fluids. The rotating gears develop a liquid seal with the pump casing and create a vacuum at the pump inlet. Fluid, drawn into the pump, is enclosed within the cavities of the rotating gears and transferred to the discharge. A gear pump delivers a smooth pulse-free flow proportional to the rotational speed of its gears. There are two basic designs of gear pump: internal and external (Figure 1). An internal gear pump has two interlocking gears of different sizes with one rotating inside the other. An external gear pump consists of two identical, interlocking gears supported by separate shafts. Generally, one gear is driven by a motor and this drives the other gear (the idler). In some cases, both shafts may be driven by motors. The shafts are supported by bearings on each side of the casing. This article describes plastic gear pump in more detail. There are three stages in an internal gear pump’s working cycle: filling, transfer and delivery (Figure 2). As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing. The trapped fluid is moved from the inlet, to the discharge, around the casing. As the teeth of the gears become interlocked on the discharge side of the pump, the volume is reduced and the fluid is forced out under pressure. No fluid is transferred back through the centre, between the gears, because they are interlocked. Close tolerances between the gears and the casing allow the pump to develop suction at the inlet and prevent fluid from leaking back from the discharge side (although leakage is more likely with low viscosity liquids). External gear pump designs can utilise spur, helical or herringbone gears (Figure 3). A helical gear design can reduce pump noise and vibration because the teeth engage and disengage gradually throughout the rotation. However, it is important to balance axial forces resulting from the helical gear teeth and this can be achieved by mounting two sets of ‘mirrored’ helical gears together or by using a v-shaped, herringbone pattern. With this design, the axial forces produced by each half of the gear cancel out. Spur gears have the advantage that they can be run at very high speed and are easier to manufacture. Gear pumps are compact and simple with a limited number of moving parts. They are unable to match the pressure generated by reciprocating pumps or the flow rates of centrifugal pumps but offer higher pressures and throughputs than vane or lobe pumps. External gear pumps are particularly suited for pumping water, polymers, fuels and chemical additives. Small external gear pumps usually operate at up to 3500 rpm and larger models, with helical or herringbone gears, can operate at speeds up to 700 rpm. External gear pumps have close tolerances and shaft support on both sides of the gears. This allows them to run at up to 7250 psi (500 bar), making them well suited for use in hydraulic power applications. Since output is directly proportional to speed and is a smooth pulse-free flow, external gear pumps are commonly used for metering and blending operations as the metering is continuous and the output is easy to monitor. The low internal volume provides for a reliable measure of liquid passing through a pump and hence accurate flow control. They are also used extensively in engines and gearboxes to circulate lubrication oil. External gear pumps can also be used in hydraulic power applications, typically in vehicles, lifting machinery and mobile plant equipment. Driving a gear pump in reverse, using oil pumped from elsewhere in a system (normally by a tandem pump in the engine), creates a motor. This is particularly useful to provide power in areas where electrical equipment is bulky, costly or inconvenient. Tractors, for example, rely on engine-driven external gear pumps to power their services. External gear pumps can be engineered to handle aggressive liquids. While they are commonly made from cast iron or stainless steel, new alloys and composites allow the pumps to handle corrosive liquids such as sulphuric acid, sodium hypochlorite, ferric chloride and sodium hydroxide. What are the limitations of a gear pump? External gear pumps are self-priming and can dry-lift although their priming characteristics improve if the gears are wetted. The gears need to be lubricated by the pumped fluid and should not be run dry for prolonged periods. Some gear pump designs can be run in either direction so the same pump can be used to load and unload a vessel, for example. The close tolerances between the gears and casing mean that these types of pump are susceptible to wear particularly when used with abrasive fluids or feeds containing entrained solids. External gear pumps have four bearings in the pumped medium, and tight tolerances, so are less suited to handling abrasive fluids. For these applications, universal gear pump are more robust having only one bearing (sometimes two) running in the fluid. A gear pump should always have a strainer installed on the suction side to protect it from large, potentially damaging, solids. Generally, if the pump is expected to handle abrasive solids it is advisable to select a pump with a higher capacity so it can be operated at lower speeds to reduce wear. However, it should be borne in mind that the volumetric efficiency of a gear pump is reduced at lower speeds and flow rates. A gear pump should not be operated too far from its recommended speed. For high temperature applications, it is important to ensure that the operating temperature range is compatible with the pump specification. Thermal expansion of the casing and gears reduces clearances within a pump and this can also lead to increased wear, and in extreme cases, pump failure. Despite the best precautions, gear pumps generally succumb to wear of the gears, casing and bearings over time. As clearances increase, there is a gradual reduction in efficiency and increase in flow slip: leakage of the pumped fluid from the discharge back to the suction side. Flow slip is proportional to the cube of the clearances between the cog teeth and casing so, in practice, wear has a small effect until a critical point is reached, from which performance degrades rapidly. Gear pumps continue to pump against a back pressure and, if subjected to a downstream blockage will continue to pressurise the system until the pump, pipework or other equipment fails. Although most gear pumps are equipped with relief valves for this reason, it is always advisable to fit relief valves elsewhere in the system to protect downstream equipment. The high speeds and tight clearances of external gear pumps make them unsuitable for shear-sensitive liquids such as foodstuffs, paint and soaps. Internal gear pumps, operating at lower speed, are generally preferred for these applications. What are the main applications for gear pumps? External gear pumps are commonly used for pumping water, light oils, chemical additives, resins or solvents. They are preferred in any application where accurate dosing is required such as fuels, polymers or chemical additives. The output of a gear pump is not greatly affected by pressure so they also tend to be preferred in any situation where the supply is irregular. Summary An external gear pump moves a fluid by repeatedly enclosing a fixed volume within interlocking gears, transferring it mechanically to deliver a smooth pulse-free flow proportional to the rotational speed of its gears. External gear pumps are commonly used for pumping water, light oils, chemical additives, resins or solvents. They are preferred in applications where accurate dosing or high pressure output is required. External gear pumps are capable of sustaining high pressures. The tight tolerances, multiple bearings and high speed operation make them less suited to high viscosity fluids or any abrasive medium or feed with entrained solids. External-gear pumps are rotary, positive displacement machines capable of handling thin and thick fluids in both pumping and metering applications. Distinct from internal-gear pumps which use “gear-within-a-gear” principles, external-gear pumps use pairs of gears mounted on individual shafts. They are described here along with a discussion of their operation and common applications. For information on other pumps, please see our Pumps Buyers Guide. Spur gear pumps Spur gear pumps use pairs of counter-rotating toothed cylinders to move fluid between low-pressure intakes and high-pressure outlets. Fluid is trapped in pockets formed between gear teeth and the pump body until the rotating gear pairs bring individual elements back into mesh. The decreasing volume of the meshing gears forces the fluid out through the discharge port. A relatively large number of teeth minimizes leakage as the gear teeth sweep past the pump casing. Spur gear pumps can be noisy due to a certain amount of fluid becoming trapped in the clearances between meshing teeth. Sometimes discharge pockets are added to counteract this tendency. Spur gear pumps are often fitted with sleeve bearings or bushings which are lubricated by the fluid itself—usually oil. Other fluids that lack oil’s lubricity generally demand more stringent pump designs, including locating bearings outside of the wetted cavities and providing appropriate seals. Dry-running bearings are sometimes used. The use of simply-supported shafts (as opposed to cantilevered arrangements seen in many internal gear designs) makes for a robust pump assembly capable of handling very thick liquids, such as tar, without concern for shaft deflection. Helical gear pumps Similar to the spur gear pump, the helical gear pump uses a pair of single- or double-helical (herringbone) gears. Helical gears run quieter than spur gears but develop thrust loads which herringbone gears are intended to counteract. These designs are often used to move larger volumes than spur gear pumps. Helical gears produce fewer pulsations than stainless gear pump as the meshing of teeth is more gradual compared with spur-gear designs. Helix angles run between 15 and 30°. Both the helical and herringbone gear pumps eliminate the problem of trapping fluid in the mesh. These designs can introduce leakage losses where the teeth mesh, however, unless very tight tooth clearances are maintained. The higher manufacturing costs associated with herringbone gear pumps must be balanced against their improved performance. Applications External-gear pumps can pump fluids of nearly any viscosity, but speed must normally be reduced for thicker materials. A typical helical gear pump might run at 1500 rpm to move a relatively thin fluid such as varnish but would have to drop its speed nearer to 500 rpm to pump material as thick as molasses in July. External-gear pumps generally are unsuited for materials containing solids as these can lead to premature wear, although some manufacturers make pumps specifically for this purpose, usually through the use of hardened steel gears or gears coated with elastomer. External-gear pumps are self-priming and useful in low NPSH applications. They generally deliver a smooth, continuous flow. In theory, at least, they are bi-directional. They are available as tandem designs for supplying separate or combined fluid-power systems. These pumps are capable of handling very hot fluids although the clearances must be closely matched to the expected temperatures to insure proper operation. Jacketed designs are available as well. External-gear pumps see wide applications across many industries: food manufacturers use them to move thick pastes and syrups, in filter presses, etc.; petrochemical industries deploy them in high-pressure metering applications; engine makers use them for oil delivery. They are used as transfer pumps. Special designs are available for aerospace applications. Pumps for fluid power will conform to SAE bolt-hole requirements. External-gear pumps are manufactured from a variety of materials including bronze, lead-free alloys, stainless steel, cast and ductile iron, Hastelloy, as well as from a number of non-metals. External-gear pumps can be manufactured as sanitary designs for food, beverage, and pharmaceutical service. The gears can be overhung, supported by bearings outside the housing with a variety of seals and packings available. Access to these internal pump components through a cover plate makes sanitizing straightforward. Gears are commonly manufactured from composites of PTFE and stainless steel as well as other plastics. Close-coupled and sealless designs are available. External gear pumps are the least costly of the various positive-displacement pumps but also the least efficient. Pressure imbalances between suction and discharge sides can promote early bearing wear, giving them somewhat short life expectancies. One general disadvantage that all heat preservation gear pump share over some other positive-displacement pump styles – vane pumps, for instance – is their inability to provide a variable flow rate at a given input speed. Where this is a requirement, a work-around is to use drives capable of speed control, though this is not always a practical solution. Finally, while rotary, positive-displacement pumps are capable of pumping water, their primary application is in oils and viscous liquids because of the need to keep rubbing surfaces lubricated and the difficulty in sealing very thin fluids. For most applications where water is the media, the centrifugal, or dynamic-displacement pump, has been the clearer choice.
Дата публікації: 26-09-21
Опис: Swelling kinetic study of poly(methyl vinyl ether-co-maleic acid) hydrogels as vehicle candidates for drug delivery This review highlights recent progress in the synthesis and application of vinyl ethers (VEs) as monomers for modern homo- and co-polymerization processes. VEs can be easily prepared using a number of traditional synthetic protocols including a more sustainable and straightforward manner by reacting gaseous acetylene or calcium carbide with alcohols. The remarkably tunable chemistry of VEs allows designing and obtaining polymers with well-defined structures and controllable properties. Both VE homopolymerization and copolymerization systems are considered, and specific emphasis is given to the novel initiating systems and to the methods of stereocontrol. The composition of chlorophyll-precursor pigments, particularly the contents of diethylene glycol divinyl ether, in etiolated tissues of higher plants were determined by polyethylene-column HPLC (Y. Shioi, S. I. Beale Anal Biochem 162: 493-499), which enables the complete separation of these pigments. DV-Pchlide was ubiquitous in etiolated tissue of higher plants. From the analyses of 24 plant species belonging to 17 different families, it was shown that the concentration of DV-Pchlide was strongly dependent on the plant species and the age of the plants. The ratio of DV-Pchlide to MV-Pchlide in high DV-Pchlide plants such as cucumber and leaf mustard decreased sharply with increasing age. Levels of DV-Pchlide in Gramineae plants were considerably lower at all ages compared with those of other plants. Etiolated tissues of higher plants such as barley and corn were, therefore, good sources of MV-Pchlide. Absorption spectra of the purified MV- and DV-Pchlides in ether are presented and compared. Both epoxides and vinyl ethers can be polymerized cationically albeit through different intermediates. However, in the case of epoxide-vinyl ether mixtures the exact mechanism of cationically initiated polymerization is unclear. Thus, although vinyl ethers can be used as reactive diluents for epoxides it is uncertain how they would affect their reactivity. Cationic photocuring of diepoxides has many industrial applications. Better understanding of the photopolymerization of epoxy-vinyl ether mixtures can lead to new applications of cationically photocured systems. In this work, photo-DSC and real-time Fourier Transform Infrared Spectroscopy (RT-FTIR) were used to study cationic photopolymerization of diepoxides and vinyl ethers. In the case of mixtures of aromatic epoxides with tri(ethylene glycol) divinyl ether, TEGDVE, photo-DSC measurements revealed a greatly reduced reactivity in comparison to the homopolymerizations and suggested the lack of copolymerization between aromatic epoxides and TEGDVE. On the other hand, for mixtures of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate, ECH, with TEGDVE the results indicated high reactivity of the blends. The polymerization mechanism might include copolymerization. To examine this mechanism, mixtures of the ECH with a tri(ethylene glycol) mono-vinyl ether, TEGMVE, were studied by both photo-DSC and RT-FTIR. Principal component analysis (PCA) proved to be an efficient tool in analyzing a large matrix of the spectral data from the polymerization system. PCA was able to provide insight into the reasons for the differences among replicated experiments with the same composition ratio and supported the hypothesis of copolymerization in the ECH/TEGMVE system. Thus, blends of cycloaliphatic epoxides and vinyl ethers seem to have a great potential for applications in high-productivity industrial photopolymerization processes. Vinyl acetate is an organic compound with the formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, an important industrial polymer. The worldwide production capacity of 1,4-bis(vinyloxy)-butane was estimated at 6,969,000 tonnes/year in 2007, with most capacity concentrated in the United States (1,585,000 all in Texas), China (1,261,000), Japan (725,000) and Taiwan (650,000). The average list price for 2008 was $1600/tonne. Celanese is the largest producer (ca 25% of the worldwide capacity), while other significant producers include China Petrochemical Corporation (7%), Chang Chun Group (6%), and LyondellBasell (5%). It is a key ingredient in furniture glue. It can be polymerized to give polyvinyl acetate (PVA). With other monomers it can be used to prepare various copolymers such as ethylene-vinyl acetate (EVA), vinyl acetate-acrylic acid (VA/AA), polyvinyl chloride acetate (PVCA), and polyvinylpyrrolidone (Vp/Va copolymer, used in hair gels). Due to the instability of the radical, attempts to control the polymerization by most "living/controlled" radical processes have proved problematic. However, RAFT (or more specifically, MADIX) polymerization offers a convenient method of controlling the synthesis of PVA by the addition of a xanthate or a dithiocarbamate chain transfer agent. Vinyl acetate undergoes many of the reactions anticipated for an alkene and an ester. Bromine adds to give the dibromide. Hydrogen halides add to give 1-haloethyl acetates, which cannot be generated by other methods because of the non-availability of the corresponding halo-alcohols. Acetic acid adds in the presence of palladium catalysts to give ethylidene diacetate, CH3CH(OAc)2. It undergoes transesterification with a variety of carboxylic acids. The alkene also undergoes Diels–Alder and 2+2 cycloadditions. Tests suggest that vinyl acetate is of low toxicity. Oral LD50 for rats is 2920 mg/kg. On January 31, 2009, the Government of Canada's final assessment concluded that exposure to vinyl acetate is not harmful to human health. This decision under the Canadian Environmental Protection Act (CEPA) was based on new information received during the public comment period, as well as more recent information from the risk assessment conducted by the European Union. In the context of large-scale release into the environment, it is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), under which it "does not meet toxicity criteria but because of its acute lethality, high production volume known risk is considered a chemical of concern". By this law, it is subject to strict reporting requirements by facilities that produce, store, or use it in quantities greater than 1000 pounds. To date, methods of quantum-chemical calculations have been increasingly developed. As a result, it is possible to estimate the geometry of molecules, calculate the stability of intermediate products and transition states. In the experimental method of calculating such results for most reactions, along with a multi-stage process, there are difficulties associated with the appearance of intermediate stages and the presence of intermediate reaction products in an extremely small time. Radical copolymerization of polyethylene glycol maleate with Di(ethylene Glycol) monovinyl ether of monoethanol amine has been performed for the first time. Radical co- and terpolymerization of the systems polyethylene glycol maleate with acrylamide and 1,4-butanediol monovinyl ether of monoethanol amine has been studied. Molecular weight of polyethylene glycol maleate has been determined using light scattering and gel permeation chromatography. The compositions of the polymers and copolymerization constants of the studied systems have been determined. The composition of the copolymers has been found using gas chromatography. Kinetic curves show that with increasing molar fraction of acrylamide in the solution the reaction rate and swelling capacity of the copolymers increase. It has been shown that the composition of terpolymers determined experimentally differs considerably from the one calculated taking into account obtained constants of copolymerization. Deviations found are due to various intermolecular interactions in these systems. The possibility of controlling the properties of network copolymers of polyethylene glycol maleate by changing external factors has been studied. Swelling capacity of the copolymers investigated was studied using gravimetric method. Hydrogels have been widely used for various biomedical and pharmaceutical applications due to their biocompatibility, high water content and rubbery nature, which resemble natural tissue. Polyethylene glycol (PEG) crosslinked poly(methyl diethylene glycol monovinyl ether and maleic acid) (PMVE/MA) hydrogel is widely studied as a vehicle for various types of drug delivery. It has been reported that swelling and diffusion property of hydrogel are important features for their effectiveness. Higher swelling of PMVE/MA hydrogel facilitates greater amount of drug to be delivered. However, delivery of high molecular weight drugs such as ovalbumin and bevacizumab is still a challenge with existing formulation of PMVE/MA hydrogels. This study aims to optimise PMVE/MA hydrogel formulations and determine the swelling kinetics of different hydrogel formulations. Methods PMVE/MA hydrogels were prepared by inducing esterification reaction with PEG. Each formulation of hydrogel consists of different concentration and molecular mass of PMVE/MA and PEG. Swelling kinetics of each formulation were studied by calculating % swelling and second order kinetic model was used to calculate the swelling rate constant (Ks) and degree of swelling at equilibrium (Seq). The effect of different foaming agents (Na2CO3 and NaHCO3) on the swelling of hydrogel was also studied. Results Our results shows that hydrogels synthesised from higher molecular weight 15% (w/w) PMVE/MA and 7.5 % (w/w) PEG 12,000 have 2200% swelling. The swelling of hydrogel decreased with increasing concentrations of PMVE/MA and PEG. Hydrogel mixture containing PEG 12,000 with longer polymer chains resulted in better swelling compared to PEG 10,000. Meanwhile high concentration of foaming agents (up to 3% w/w) has a positive effect on hydrogel swelling. Conclusion The hydrogels formulation containing 15% (w/w) PMVE/MA and 7.5 % (w/w) PEG 12,000 in this study yielded 1.28 times greater swelling compared to previously reported formulation. It is proposed that, this hydrogel would serve as a better vehicle candidate for macromolecular drug delivery.
Дата публікації: 26-09-21
Опис: UChicago institute helps reassemble ancient, rare art from first to 6th centuries BAMIYAN, Afghanistan — Here is a reminder to someone with the initials A.B., who on March 8 climbed inside the cliff out of which Bamiyan’s two giant Buddhas were carved 1,500 years ago. In a domed chamber — reached after a trek through a passageway that worms its way up the inside of the cliff face — A.B. inscribed initials and the date, as hundreds of others had in many scripts, then added a little heart. It’s just one of the latest contributions to the destruction of the World Heritage Site of Bamiyan’s famous Buddhas. The worst was the Taliban’s effort in March 2001, when the group blasted away at the wooden buddha statue, one 181 feet and the other 125 feet tall, which at the time were thought to be the two biggest standing Buddhas on the planet. It took the Taliban weeks, using artillery and explosive charges, to reduce the Buddhas to thousands of fragments piled in heaps at the foot of the cliffs, outraging the world. Since then, the degradation has continued, as Afghanistan and the international community have spent 18 years debating what to do to protect or restore the site, with still no final decision and often only one guard on duty. One recent idea came from a wealthy Chinese couple, Janson Hu and Liyan Yu. They financed the creation of a Statue of Liberty-size 3D light projection of an artist’s view of what the larger Buddha, known as Solsol to locals, might have looked like in his prime. The image was beamed into the niche one night in 2015; later the couple donated their $120,000 projector to the culture ministry. Editors’ Picks ‘Very Ordinary’ Astronauts Prepare for an Extraordinary Launch to Space Why Use a Dictionary in the Age of Internet Search? The Rock That Ended the Dinosaurs Was Much More Than a Dino Killer Continue reading the main story The local authorities bring it out on special occasions, but rarely, as Bamiyan has no city power supply, other than fields of low-capacity solar panels. The 3D-image projector is power-hungry and needs its own diesel generator. Most of the time, the remains of the monument are so poorly guarded that anyone can buy a ticket ($4 for foreigners, 60 cents for Afghans), walk in and do pretty much whatever he wants. And many do. Souvenir-hunters pluck pieces of painted stucco decorations from the network of chambers or take away chunks of fallen sandstone. Graffiti signatures, slogans, even solicitations for sex abound. Anyone can, as A.B. did, crawl through the passageways surrounding the towering niches in the cliff, through winding staircases tunneled into the sandstone and up steps with risers double the height of modern ones, as if built for giants. At the end of this journey, you arrive above the eastern niche, which housed the smaller Buddha, and stand on a ledge just behind where the statue’s head once was, taking in the splendid Buddha’s eye view of snow-capped mountains and the lush green valley far below. The soft sandstone of the staircases crumbles underfoot, so that the very act of climbing them is at least in part a guilty pleasure — though no longer very dangerous. Twisted iron banisters set in the stone make the steep inclines and windows over the precipices more safely navigable, if not as authentically first millennium. When the Taliban demolished the Buddhas, in an important sense they botched the job. The Buddhas, built over perhaps a century from 550 A.D. or so, were just the most prominent parts of a complex of hundreds of caves, monasteries and shrines, many of them colorfully decorated by the thousands of monks who meditated and prayed in them. Even without the Buddhas themselves, their niches remain, impressive in their own right; the Statue of Liberty would fit comfortably in the western one. Unesco has declared the whole valley, including the more than half-mile-long cliff and its monasteries, a World Heritage Site. “If the Taliban come back again to destroy it, this time they would have to do the whole cliff,” Aslam Alawi, the local head of the Afghan culture ministry, said. Unesco has also declared the Bamiyan Buddhas complex a “World Heritage Site in Danger,” one of 54 worldwide. The larger western niche is still at risk of collapsing. When the Taliban seized power in Afghanistan in 1996, they imposed an extremist version of Islamic law across the country. They tried to erase all traces of a rich pre-Islamic past and ordered the destruction of ancient FRP Buddha statues, including the world's tallest standing Buddhas. Those memories are still alive for millions of Afghans. And now they have become present concerns, as the US and Afghan government negotiate with the Taliban for a deal that could see them return to power in Afghanistan. The BBC's Shoaib Sharifi visited the National Museum in Kabul where a team are rebuilding some of the ancient Buddha sculptures that were destroyed by the Taliban. Some of the earliest known statues depicting the Buddha have him in startling costume—draped in the lushly folded fabric of ancient Greece or Rome. Sometimes he has Greco-Roman facial features, naturalistically rendered and muscled torsos, or is even shown protected by Hercules. Many of these striking Buddhas hailed from Hadda, a set of monasteries in modern-day Afghanistan where Buddhism flourished for a thousand years before the rise of Islam. Located on the Silk Road, the area had frequent contact with the Mediterranean—hence the Buddha’s Hellenistic features. One of the richest collections of this unique art from Hadda was destroyed in 2001, when the Taliban ransacked the National Museum of Afghanistan and shattered the museum’s Buddha statues. Nearly two decades later, the museum’s conservators are working with the University of Chicago’s Oriental Institute, one of the world’s foremost research centers on the civilizations of the ancient Middle East, to bring the collection back to life. Supported by cultural heritage preservation grants from the U.S. Embassy in Kabul, OI researchers, along with Afghan colleagues, are painstakingly cleaning, sorting and reassembling statues from the more than 7,500 fragments left behind, which museum employees swept up and saved in trunks in the basement. “When they were broken, we lost a part of history—an important period of high artistic achievement—which these objects represent,” said Mohammad Fahim Rahimi, director of the National Museum of Afghanistan. “They are the only pieces remaining from the archaeological sites; Hadda was burned and looted during the 1980s, so these pieces at the museum are all we have left. By reviving them, we are reviving part of our history.” RECOMMENDED STORIES Michael Rakowitz exhibit Artist reimagines ancient Middle Eastern artifact in vivid color Cleaning the Persepolis relief Ancient Persian artifact nearly 2,500 years old returns to UChicago NEWSLETTER Get more with UChicago News delivered to your inbox. The ceramic buddha statue are beautiful, by all accounts. First excavated by French archaeologists in the 1930s, and spanning 500 years of Afghanistan’s history between the first and sixth centuries A.D., they are an example of a rare art form unique to the region, often called the Gandharan style. Some stand alone and others in tableaus, ranging from life-size to others that can fit in the palm of a hand. But the task of reconstructing them is more than a puzzle. The materials these ancient artisans used were primarily limestone, schist and stucco—which tend to crumble and disintegrate under duress, rather than simply crack. “It’s more like trying to assemble pieces from 30 different jigsaw puzzles that have all been dumped together—without the pictures from the boxes,” said Gil Stein, professor at the Oriental Institute and a leading expert on the rise of social complexity in the ancient Near East. Stein heads the project, which is part of the OI’s ongoing work with the National Museum of Afghanistan Cultural Preservation Partnership. Begun in 2012, the partnership has helped restore the museum’s infrastructure, including developing a bilingual database to document the first full inventory of the museum’s collections, as well as training conservators in the latest techniques for preserving and restoring objects. The collection is largely from the Hadda monasteries located in northwestern Afghanistan, near the modern-day city of Jalalabad. The region’s warm climate fosters citrus and pomegranate trees and helped it blossom as a center of trade on the Silk Road for centuries—thus its art influenced by both East and West. ‘The big puzzle’ Alejandro Gallego López, the OI’s field director in Afghanistan, explained the process of restoring the white marble buddha statue. First is to assess the collection—identifying and classifying features, such as archaeological motifs, and visible parts of bodies, like legs, heads or arms. This census can help them estimate how many objects there were originally (they think it was between 350 and 500).
Дата публікації: 26-09-21
Опис: How Fuel Injection Systems Work In trying to keep up with emissions and fuel efficiency laws, the fuel system used in modern cars has changed a lot over the years. The 1990 Subaru Justy was the last car sold in the United States to have a carburetor; the following model year, the Justy had fuel injection. But fuel injection has been around since the 1950s, and electronic fuel injection was used widely on European cars starting around 1980. Now, all cars sold in the United States have fuel injection systems. In this article, we'll learn how the fuel gets into the cylinder of the engi-ne, and what terms like "multi-port fuel injection" and "throttle body fuel injection" mean. -For most of the existence of the internal combustion engine, the carburetor has been the device that supplied fuel to the engine. On many other machines, such as lawnmowers and chainsaws, it still is. But as the automobile evolved, the carburetor got more and more complicated trying to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits: Main circuit - Provides just enough fuel for fuel-efficient cruising Idle circuit - Provides just enough fuel to keep the engine idling Accelerator pump - Provides an extra burst of fuel when the accelerator pedal is first depressed, reducing hesitation before the engine speeds up Power enrichment circuit - Provides extra fuel when the car is going up a hill or towing a trailer Choke - Provides extra fuel when the engine is cold so that it will start In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop control -- it was not feasible to achieve this control with carburetors. There was a brief period of electrically controlled carburetors before fuel injection systems took over, but these electrical carbs were even more complicated than the purely mechanical ones. At first, carburetors were replaced with throttle body FIAT fuel injector systems (also known as single point or central fuel injection systems) that incorporated electrically controlled fuel-injector valves into the throttle body. These were almost a bolt-in replacement for the carburetor, so the automakers didn't have to make any drastic changes to their engine designs. Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel injection (also known as port, multi-point or sequential fuel injection). These systems have a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and quicker response. When You Step on the Gas The gas pedal in your car is connected to the throttle valve -- this is the valve that regulates how much air enters the engine. So the gas pedal is really the air pedal. When you step on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU, the computer that controls all of the electronic components on your engine) "sees" the throttle valve open and increases the fuel rate in anticipation of more air entering the engine. It is important to increase the fuel rate as soon as the throttle valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as some air reaches the cylinders without enough fuel in it. Sensors monitor the mass of air entering the engine, as well as the amount of oxygen in the exhaust. The ECU uses this information to fine-tune the fuel delivery so that the air-to-fuel ratio is just right. -In order to provide the correct amount of fuel for every operating condition, the e-ngine control unit (ECU) has to monitor a huge number of input sensors. Here are just a few: Nox sensor - Tells the ECU the mass of air entering the engine Oxygen sensor(s) - Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load) Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced. Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse width There are two main types of control for multi-port systems: The fuel injectors can all open at the same time, or each one can open just before the intake valve for its cylinder opens (this is called sequential multi-port fuel injection). The advantage of sequential vw fuel injector is that if the driver makes a sudden change, the system can respond more quickly because from the time the change is made, it only has to wait only until the next intake valve opens, instead of for the next complete revolution of the engine. Engine Controls and Performance Chips --The algorithms that control the engine are quite complicated. The software has to allow the car to satisfy emissions requirements for 100,000 miles, meet EPA fuel economy requirements and protect engines against abuse. And there are dozens of other requirements to meet as well. The engine control unit uses a formula and a large number of lookup tables to determine the pulse width for given operating conditions. The equation will be a series of many factors multiplied by each other. Many of these factors will come from lookup tables. We'll go through a simplified calculation of the fuel injector pulse width. In this example, our equation will only have three factors, whereas a real control system might have a hundred or more. Pulse width = (Base pulse width) x (Factor A) x (Factor B) In order to calculate the pulse width, the ECU first looks up the base pulse width in a lookup table. Base pulse width is a function of engine speed (RPM) and load (which can be calculated from manifold absolute pressure). Let's say the engine speed is 2,000 RPM and load is 4. We find the number at the intersection of 2,000 and 4, which is 8 milliseconds. From this example, you can see how the control system makes adjustments. With parameter B as the level of oxygen in the exhaust, the lookup table for B is the point at which there is (according to engine designers) too much oxygen in the exhaust; and accordingly, the ECU cuts back on the fuel. Real control systems may have more than 100 parameters, each with its own lookup table. Some of the parameters even change over time in order to compensate for changes in the performance of engine components like the catalytic converter. And depending on the engine speed, the ECU may have to do these calculations over a hundred times per second. Performance Chips This leads us to our discussion of performance chips. Now that we understand a little bit about how the control algorithms in the ECU work, we can understand what performance-chip makers do to get more power out of the engine. Performance chips are made by aftermarket companies, and are used to boost engine power. There is a chip in the ECU that holds all of the lookup tables; the performance chip replaces this chip. The tables in the performance chip will contain values that result in higher fuel rates during certain driving conditions. For instance, they may supply more fuel at full throttle at every engine speed. They may also change the spark timing (there are lookup tables for that, too). Since the performance-chip makers are not as concerned with issues like reliability, mileage and emissions controls as the carmakers are, they use more aggressive settings in the fuel maps of their performance chips. For more information on RENAULT fuel injector systems and other automotive topics, check out the links on the next page. The call for reduction in pollution has been mandated by government′s policies worldwide. This challenges the engine manufacturer to strike an optimum between engine performance and emissions. However with growing technology in the field of fuel injection equipment, the task has become realizable. For past few years it has been the hot topic to improve combustion and emissions of compression ignition engines through optimizing the fuel injection strategies. Choosing between various injection strategies are potentially effective techniques to reduce emission from engines as injection characteristics have great influences on the process of combustion. For example, increasing the fuel injection pressure can improve the fuel atomization and subsequently improve the combustion process, resulting in a higher brake thermal efficiency, producing less HC, CO, PM emissions, but more NOx emission. Pilot injection help in reducing combustion noise and NOx emissions and immediate post injection may help in soot oxidation and late post injection helps in regeneration of diesel particulate filter. This article aims at a comprehensive review of various fuel injection strategies viz varying injection pressure, injection rate shapes, injection timing and split/multiple injections for engine performance improvement and emissions control. Although every strategy has its own merits and demerits, they are explained in detail, in view of helping researchers to choose the better strategy or combination for their applications.
Дата публікації: 26-09-21