Lyophobic colloids, see Colloid

When considering how the evolution of life could have come about, the seeding of terrestrial life by extraterrestrial bacterial spores traveling through space (panspermia) deserves mention. Much is said about the possibility of some form of life on other planets, including Mars or more distant celestial bodies. Is it possible for some remnants of bacterial life, enclosed in a protective coat of rock dust, to have traveled enormous distances, staying dormant at the extremely low temperature of space and even surviving deadly radiation The spore may be neither alive nor completely dead, and even after billions of years it could have an infinitesimal chance to reach a planet where liquid water could restart its life. Is this science fiction or a real possibility We don t know. Around the turn of the twentieth century Svante Arrhenius (Nobel Prize in chemistry 1903) developed this theory in more detail. There was much recent excitement about claimed fossil bacterial remains in a Martian meteorite recovered from Antarctica (not since  [c.16]

Being fairly strong willed, I was determined to continue my life with as few distractions as possible. Thus I was back at my university duties the day after our return from Stockholm. Research and teaching were always an integral part of my life, not just a work habit, and 1 could not see any reason for change. I also did not feel ready for retirement, formal or de facto, while pretending otherwise. I like teaching and still feel able to contribute significantly to research. In short, I felt disinclined to rest on past laurels.  [c.186]

Salt is an essential nutrient without which life could not exist (see Mineral nutrients). Sodium is the principal cation in blood plasma and body tissue fluids. Regulation of sodium in the body maintains osmotic pressure, acid—base balance, and volume of circulating body fluids (11). Extracellular fluid volume is maintained by the total body sodium content. Brain mechanisms control the elective intake of salt, and physiological control systems regulate the conservation and excretion of sodium. The human body contains about 1840 mg (80 mEq) of sodium per kilogram of body weight, half of which is exchangeable (12). The sodium concentration of blood and other body fluids is maintained by a complex mechanism involving the kidneys and the adrenal glands. Renal excretion of sodium can be controlled so that a wide range of Na intakes can be accommodated. Sodium is conserved when intake is low, and excreted when intake is high. Chloride, too, is essential to good health. It preserves acid—base balance in the body, aids potassium absorption, suppHes the essence of digestive stomach acid, and enhances the abiUty of the blood to carry carbon dioxide from respiring tissues to the lungs.  [c.185]

Butter is used in some, usually more expensive, bakery foods, and is prized for its flavor contribution. Fats are used in some products such as pie cmst, croissants, or puff pastry, up to 60%, based on flour. StabiHty of fats and oils in perishable items such as breads, cakes, or pastries is of no consequence because shelf life is so limited that rancidity does not occur. In cookies and crackers, however, stable fats must be used in the formula since prolonged shelf life could lead to product deterioration with fats that develop rancidity.  [c.461]

As shown in Figure la, the basic element of the H2S /H2O process is a pair of gas—Hquid contacting towers each containing a number of sieve or bubble-cap plates (see Distillation). The cold tower operates at a temperature of 30°C and the hot tower at 120—140°C. Water entering this system flows downward through the cold tower and then through the hot tower countercurrent to a stream of hydrogen sulfide gas at 1896 kPa (275 psig). The water is progressively enriched in deuterium as it passes through the cold tower, and progressively depleted as it passes through the hot tower, eventually leaving the hot tower at a concentration below that at which it entered the system. The HDO and HDS that build up within the process are withdrawn from the base of the cold tower and top of the hot tower, respectively, by withdrawing a fraction of the water and gas flow. These enriched fractions are fed to a succeeding stage for further concentration. The hydrogen sulfide gas, which acts as a transport medium for the deuterium, circulates in a closed loop within the several stages of the process. About 20% of the deuterium in natural water can be economically extracted in this manner.  [c.7]

It is well established that processes involved in differentiation of the male reproductive tract and masculinisation of genitalia during fetal and neonatal life are controlled by hormones and constitute a vulnerable period of development. It is obvious that any disruption of these processes could have serious implications for future fertility. A variety of data is accumulating which suggests that male reproductive health is declining, some of which is widely accepted (the testis cancer data) and some of which remains controversial (semen quality data). At present the only sensible (and most cautious) option is to treat the situation with concern and to perform prospective studies to establish whether men really are at risk. However, this will not give an answer for another 10-20 years, by which time male reproduction may be severely compromised. In the meantime, studies must continue to address whether endocrine disrupters present in the environment are capable of adversely affecting the health of humans and wildlife. It remains a plausible hypothesis that inappropriate exposure to oestrogen during development could have permanent consequences which might impair fertility. However, this is only one mechanism by which the endocrine system may be perturbed and investigation of other mechanisms should not be neglected, as any compound which can mimic hormone action either as an agonist or antagonist, or interfere with the biosynthesis or metabolism of both androgen and oestrogen and their receptors, has the ability to be an endocrine disruptor.  [c.108]

Steitz has suggested that DNA bending by CAP could contribute to activation of transcription by looping the DNA around CAP to provide for contacts between RNA polymerase and DNA upstream of the CAP-binding site. Such a model could explain how CAP can activate transcription from a variety of distances from the RNA polymerase-binding site since the size of the loop could vary.  [c.147]

During operation the slurry is pumped under pressure into a vessel that is fitted with a stack of vertical leaves that serve as filter elements. Each leaf has a centrally located neck at its bottom which is inserted into a manifold that collects the filtrate. The leaf is constructed with ribs on both sides to allow free flow of filtrate towards the neck and is covered with coarse mesh screens that support the finer woven metal screens or filter cloth that retain the cake. The space between the leaves may  [c.196]

Other examples exist where different factors on the list of material selection factors in Figure 7-20 are the design drivers. However, at the time of the initial applications of advanced composite materials, the main issues were simply strength and stiffness. Perhaps a fatigue-life issue could be more important in some applications. Some applications are made despite some disadvantages for composite materials in some of these material selection factors. For example, the electrical conductivity of graphite-epoxy is not sufficient when designing an aircraft subject to a lightning strike (as are all aircraft). All parts of an aircraft must be able to dissipate the electrical charges of lightning strikes. Thus, some supplementary material or electrically conductive material systems must be added to the graphite-epoxy in order to provide the aircraft with appropriate lightning-resistant characteristics.  [c.391]

Other examples exist where different factors on the list of material selection factors in Figure 7-20 are the design drivers. However, at the time of the initial applications of advanced composite materials, the main issues were simply strength and stiffness. Perhaps a fatigue-life issue could be more important in some applications. Some applications are made despite some disadvantages for composite materials in some of these material selection factors. For example, the electrical conductivity of graphite-epoxy is not sufficient when designing an aircraft subject to a lightning strike (as are all aircraft). All parts of an aircraft must be able to dissipate the electrical charges of lightning strikes. Thus, some supplementary material or electrically conductive material systems must be added to the graphite-epoxy in order to provide the aircraft with appropriate lightning-resistant characteristics.  [c.391]

There is a danger in relying on least-squares regression analysis without graphic presentation of the data. The human eye, in combination with chemical knowledge, is a more subtle qualitative judge of data than is regression analysis. Observe Fig. 2-11, a first-order plot of the hydrolysis of p-nitrophenyl glutarate in the presence of p-methoxycinnamate ion. The straight line has been drawn through the points in the first half-life, and it reveals a distinct curvature in the later portion of the reaction. Least-squares analysis without an accompanying plot might overlook this small but real effect. (In this case the curvature could be easily accounted for The pH changed by about -I- 0.03 unit during the course of the reaction, resulting in erroneous i4, and, especially, /loo values, because the proportion of product in the absorbing form is very sensitive to pH at the pH of the experiment.) The availability  [c.52]

Cold Habitats. Because of considerations of surface area relative to body mass, animals that live in cold habitats tend to have larger body sizes and smaller extremities (especially ears and legs) compared to their counterparts in warmer habitats. Animals that live in cold habitats also have a greater amount of insulation, such as fat, fur, or feathers. Behavioral adaptations include gathering in groups, which effectively decreases the exposed surface area of each individual.  [c.185]

Greases with a mixed base are not shown in the table because, in general, they are characterized by the predominant base for example, a soda-lime grease behaves like a soda grease. The required length of service may modify temperature limits. Thus, if soda grease requires having only a short life, it could be used at temperatures up to 120°C (250°F).  [c.880]

The first reaction is exothermic, and the second is endothermic. Overall, the reaction evolves considerable heat. Figure 2.7 shows two alternative reactor designs. Figure 2.1a shows a shell and tube type of device which generates steam on the shell side. The temperature profile through the reactor in Fig. 2.7a is seen to be relatively smooth. Figure 2.76 shows an alternative reactor design that uses cold-shot cooling. By contrast with the tubular reactor, the cold-shot reactor shown in Fig. 2.76 experiences significant temperature fluctuations. Such fluctuations can cause accidental catalyst overheating and shorten catalyst life.  [c.56]

The thermal profile through the reactor will in most circumstances be carefully optimized to maximize selectivity, extend catalyst life, etc. Because of this, direct heat integration with other process streams is almost never carried out. The heat transfer to or from the reactor is instead usually carried out by a heat transfer intermediate. For example, in exothermic reactions, cooling might occur by boiling water to raise steam, which, in turn, can be used to heat cold streams elsewhere in the process.  [c.327]

If changes to the reactor design are possible, then the simple criteria introduced in Chap. 12 can be used to direct those changes. Heat integration will always benefit by making hot streams hotter and cold streams colder. This applies whether the heat integration is carried out directly between process streams or through an intermediate such as steam. For example, consider the exothermic reactions in Fig. 13.1a. Allowing the reactor to work at higher temperature improves the heat integration potential if this does not interfere with selectivity or catalyst life or introduce safety and control problems, etc. However, if the reactor must work with a fixed intermediate cooling fluid, such as steam generation, then the only benefit will be a reduced heat transfer area in the reactor. The steam becomes a hot stream available for heat integration after leaving the reactor. If the pressure of steam generation can be increased, making a hot stream hotter, then there may be energy or area benefits when it is integrated with the rest of the process.  [c.338]

Volumetric estimates are required at all stages of the field life cycle. In many instances a first estimate of how big an accumulation could be is requested. If only a back of the envelope estimate is needed or if the data available is very sparse a quick look estimation can be made using field wide averages.  [c.153]

Operating strategies and product quality should be carefully reassessed to determine whether less treatment and more downtime can be accommodated and what cost saving this could make. Many facilities are constructed with high levels of built-in redundancy to minimise production deferment early in the project life. Living with periodic shutdowns may prove to be more cost effective in decline. Intermittent production may also reduce treatment costs by using gravity segregation in the reservoir to reduce water cuts or gas influx, as mentioned in Section 15.4.  [c.367]

Generally the signal to noise ratio can be enhanced by inereasing the exeitation field. But especially at higher frequencies the signal amplitude, the SQUID can amplify, is restricted by the speed - so called slew rate - of the flux locked loop. This rate is determined by the flux to voltage conversion of the SQUID. With a conversion factor of about 100 pV/tbo we could manage a gradient field ehange of about 10"  [c.301]

The introduction of automated scanning systems was a great leap forward in the development. That way, the uncertainties of manual probe guidance were eliminated. Usually, these systems were designed for high-frequency surface tests and followed the outer profile of the surface with a probe that could be moved in several axes. A continuous 100 % scan became possible and, as a result, the documentation of the tests with stripchart recorders suggested itself. Now for the first time, wheel testing became retraceable.  [c.306]

The second task is then analysing the results of the scan. The results can be displayed live on a display screen, or stored and presented all at once or after further scaling and analysis. This playback feature of sample data will be the subject of the remainder of the paper, for as we will see the playback need not be immediate nor on site, but could take place synchronously or asynchronously over the Internet.  [c.1018]

The complete loop is shown in Figure 23 It has five phase-inverting reactions, and therefore is a phase-inverting loop. The degeneracy that lies within the loop is the symmetric Dji, structure—at this symmetry all five type-I structures are degenerate. Alternatively, the five B structures could serve as anchors, the transitions between any pair are also phase inverting, with the Aj structures functioning as transition states. This example emphasizes the cardinal importance of spin pairing as the basis for choosing anchors—the conventional choice is a nuclear stmcture that lies in an energy minimum, but this is not an essential requirement.  [c.360]

The boat is then transferred to the balance pan (narrow-ended meta tweezers are most suitable for this purpose) and weighed the weight of the empty boat should never vary by more than o i mg. during its working life. The boat is transferred to the grooved block (removed from the desiccator) and 20-25 mg. of the sample to be analysed are then transferred to it. This is best carried out using a very small, narrow-ended spatula, and it is essential that only a small amount of material is put in the boat at a time—the 20-25 mg. should be transferred in several operations. The boat is then gripped firmly with the tweezers and carefully tapped on the aluminium block this serves to remove any small particles of substance that may possibly be adhering to the outside of the boat and also to settle the charge of substance thinly and evenly along the whole length of the boat. The face and groove of the block are then carefully wiped with a polishing cloth. The boat is transferred to the balance pan and reweighed. It is then returned to the block and both replaced in the desiccator.  [c.477]

SQUID sensor The SQUID converter and the coupling coil are thin film devices prepared of the high temperature superconductor Y]Ba2Cu307 on SrTiOs substrates. Typical substrate dimensions are 10 mm by 10 mm In one version, fig.4, the SQUID converter and the coupling coil are integrated on one substrate to improve the coupling in another version two substrates have been apphed and the magnetic coupling has been made by a flip chip technique. This results in a looser coupling on the one hand but a much simpler preparation process on the other hand. The SQUID converter is a one layer device applying an artificial crystalline grain boundary on a bicrystalline substrate for the preparation of the Josephson junctions. A flux to voltage conversion of about lOOpV/Oo could be obtained. A first stage of the flux  [c.300]

Inasmuch as the service life of a system is affected more by the range of stress variation than by the magnitude of stress at a given time, no credit for cold spring is permitted in stress-range calculations. However, in calculating the thrusts and moments when ac tual reactions as well as their range of variations are significant, credit is given for cold spring.  [c.995]

Automated sludge withdrawal controls are usually based on the sludge bed level. These can operate in on-off or continuous modes and will use either single-point or continuous sludge level indication sensors. In many applications, automated control of underflow withdrawal does not provide an advantage, since so few settled solids are produced that it is only necessary to remove sludge for a short interval once a day, or even less frequently. In apphcations in which the underflow is recirculated internaUy within the feedwell, it is necessaiy to maintain sufficient sludge inventoiy for the recirculation turbine to puU from. This could be handled in an automated system with a single-point low sludge bed level sensor in conjunction with a low-level arm or pump shutoff solenoid. Some applications require continuous external recirciJation of the underflow direc t to the feedweU or external reaction tanks, and an automated control loop could be used to maintain recirculation based on flow measurement, with a manually adjusted setpoint.  [c.1689]

The material properties of window glass are summarised in Table 18.1. To use these data to calculate a safe design load, we must assign an acceptable failure probability to the window, and decide on its design life. Failure could cause injury, so the window is a critical component we choose a failure probability of 10The vacuum system is designed for intermittent use and is seldom under vacuum for more than 1 hour, so the design life under load is 1000 hours.  [c.191]

The processing of biological materials and employing biological agents such as cells, enzymes, or antibodies are the principal domain of biochemical engineering. Biochemical reactions involve both cellular and enzymatic processes and the principal differences between the biochemical and chemical reactions lie in the nature of the living systems. Small living creatures known as microorganisms interact in many ways with human activities. Microorganisms play a primary role in the capture of energy from the sun. Additionally, their biological activities also complete critical segments of the cycles of carbon, oxygen, nitrogen, and other elements necessary for life. The cell is the unit of life, and cells in multi-cellular organism function together with other specialized cells. Generally, all cells possess basic common features. Every cell contains cytoplasm, a colloidal system of large biochemicals in a complex solution of smaller organic molecules and inorganic salts. The use of cells or enzymes taken from cells is restricted to conditions at which they operate, although most plant and animal cells live at moderate temperatures but cannot tolerate extremes of pH. In contrast, many microorganisms operate under mild conditions, some perform at high temperatures, others at low temperatures and also pH values, which exceed neutrality. Some can tolerate concentrations of chemicals that can be highly toxic in other cells. Thus, successful operation depends on acquiring the correct organisms or enzymes while preventing the entry of foreign organisms, which could impair the process.  [c.830]

Diabetes is a disorder of carbohydrate metabolism traceable to deficiencies in the production of insulin by the pancreas. Prior to the discovery of insulin by Banting and Best in the 1930s, the lifespan of a young diabetic was limited indeed. The finding that those diabetics whose disease began early in life could be maintained on insulin from animal sources was dramatic. A goodly number of diabetics do not manifest the disease until well into their forties. Such patients may be controlled for some time by diet or by insulin. The finding that some of the sulfonamide antibiotics could lower blood sugar in some individuals (hypoglycemia) led to the development of an additional method for treatment of the hyperglycemia of adult-onset diabetes. (It should be noted that the drug is without effect on individuals lacking capacity to produce insulin—the youthful diabetics),  [c.136]

Figure 10.4 shows a schematic representation of the multidimensional GC-IRMS System developed by Nitz et al. (27). The performance of this system is demonstrated with an application from the field of flavour analysis. A Siemens SiChromat 2-8 double-oven gas chromatograph equipped with two FIDs, a live-T switching device and two capillary columns was coupled on-line with a triple-collector (masses 44,45 and 46) isotope ratio mass spectrometer via a high efficiency combustion furnace. The column eluate could be directed either to FID3 or to the MS by means of a modified Deans switching system .  [c.226]

Probably evei-y reader has heard of the mythical incandescent lightbulb that has burned for more than fifty years. Because we are all susceptible to believing conspiracy theories, we are suspicious that manufacturers could make all lightbulbs last that long, if only they would. Most inexpensive incandescent lamps available in stores are rated for 750 hours of operation. In reality, an incandescent lamp can be made to last a vei y long time, certainly longer than 75(1 hours, but there is no free lunch. Incandescent lamp life can be prolonged considerably if the lamp is operated at low temperatures. Lamps operated at low temperatures, however, produce relatively more heat than light, so the efficacy drops below the rated 10 to 12 lumens per watt. Lamp life could also be improved if the lamp were more expensive. Incandescent lamps used m traffic signals are rated at about 8,000 hours of operation but are approximately five to ten times as expensive as the conventional household incandescent lamp, because of their more durable filament construction. An incandescent lamp can have long life, high efficacy, or low cost, but not all three at the same time. So although the mythical lamp may exist, and indeed it can be made, physics demands that it must either produce light expensively or inefficiently, and probably both.  [c.716]

It IS reasonably certain that Thomas Newcomen was born in late Januaiy or early Februai y 1663 in the family house in Dartmouth in Devon, England. He was schooled at home by the well-known nonconformist scholar, John Flavell, who played a key role in Newcomen s educational thinking. Although throughout his life Newcomen was proud of his common status as an ironmonger, some rivals attempted to credit his success to no more than good luck and chance. Many of his contemporaries doubted that he could be the sole author of so momentous an invention.  [c.843]

My deepest thanks, of course, goes to my family to my mom and dad, Sara [c.830]

The change in heat duties around the loop maintains the network heat balance and the supply Euid target temperatures of the streams. However, the temperatures around the loop change, and hence the temperature differences of the exchangers in the loop change in addition to their duties. The magnitude of U could be changed to different values and the network sized and costed at each value to find the optimal setting for U. If the optimal setting for U turns out to be 6.5 MW (the original duty on unit E), then the duty on unit E becomes zero, and this unit should be removed from the design.  [c.392]

In a completely homogenous unfaulted reservoir a single well might, in theory, drain all the reserves, though over a very long period of time. Field development plans address the compromise between well numbers, production profiles, equipment life and the time value of money. Compared to the base case development plan, additional wells may access reserves which would not necessarily be produced within the field economic lifetime, simply because the original wells were too far apart. This is illustrated in Figure 15.3 by considering the pressure distribution in a reservoir under depletion drive. A third well in this situation could recover additional reserves before the wells reach their abandonment pressure. The additional well would have to be justified economically the incremental recovery alone does not imply that the third well is attractive.  [c.352]

Infonnation, like energy, is an irreducible concept, but is surjDrisingly rarely mentioned in textbooks of biophysical chemistry (whereas bioenergetics has developed into a distinct field of its own). Yet infonnation is maybe even more gennane tlian energy to tire very essence of life, starting witli tire DNA which, it is often stated, encodes our organism, initially via tire amino acid sequence which encodes protein stmcture, and so on. The neologism bioinfonnatics usually denotes the analysis of DNA sequences, in particular tlie comparison of sequences derived from different organisms but apparently encoding tlie same protein. That tliis is a very difficult task is well illustrated by tlie analysis of transcriptional promoter sequences (to which a protein must bind in order for transcription to be initiated), which have few discernible common features which could be used to identify tliem.  [c.2843]

Once it entered production mode, the strengths and weaknesses of the NAMD design could be determined. C++, message-driven execution, and the concept of patches had each proven their utility and the program performed well on small numbers of processors. There were also some problems. Load balancing was hampered because most of the work was concentrated in a few patches near the center of the system (simulations lacked periodic boundary conditions). A patch with multiple neighbors on the same node would send several identical messages to that node the workaround for this unnecessarily complicated the communication system. Finally, it was found that a patchcentric flow of control created a mixing of the essentially serial simulation algorithm with the parallel logic for responding to incoming messages, obfuscating both and requiring an understanding of the message structure in order to make trivial modifications to the iterative loop. For these reasons, it was decided that a major redesign was necessary and work began on NAMD 2.  [c.476]

The most common gold compounds are auric chloride and chlorauric acid, the latter being used in photography for toning the silver image. Gold has 18 isotopes 198Au, with a half-life of 2.7 days, is used for treating cancer and other diseases. Disodium aurothiomalate is administered intramuscularly as a treatment for arthritis. A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). Gold is available commercially with a purity of 99.999+%. For many years the temperature assigned to the freezing point of gold has been 1063.0G this has served as a calibration point for the International Temperature Scales (ITS-27 and ITS-48) and the International Practical Temperature Scale (IPTS-48). In 1968, a new International Practical Temperature Scale (IPTS-68) was adopted, which demands that the freezing point of gold be changed to 1064.43G. The specific gravity of gold has been found to vary considerably depending on temperature, how the metal is precipitated, and cold-worked.  [c.143]

See pages that mention the term Lyophobic colloids, see Colloid : [c.50]    [c.144]    [c.702]    [c.442]    [c.537]    [c.312]    [c.426]    [c.509]    [c.536]    [c.1716]    [c.2616]    [c.10]    [c.233]   
Physical chemistry of surfaces (0) -- [ c.0 ]