Fast Effects

Nonthermal fissions are due to two different sources. There are first the resonance fissions which occur in the thermally fissionable fuel (such 

The supply of fast neutrons from thermal fissions occurs at a steady rate, and the source is distributed within the fuel lump in the shape of the thermal flux. The supply due to fast fissions, however, varies from one generation to the next because of cascade effects. This phenomenon can give rise to a slight augmentation of the fast-neutron population, depending on the properties of the fuel lump. The cascade effect may be described in terms of the collision probabilities and the fast- 

It is understood that the sequence of n fast-fission generations was initiated by a single fast neutron produced by a thermal fission. With the function (P , and a suitable set of fast-neutron cross sections we can define several pertinent processes which describe alternate histories for each neutron appearing in the nth generation. These are  

the subscript i denotes any one of the following nuclear reactions inelastic scattering radiative capture 2), fission Z/, and elastic scattering 2. The symbol S denotes an appropriate total cross section for the fast neutrons it is defined by [cf. Eq. (2.50)] 

Consider now the history of neutrons produced in the first generation of fast fission. The number (Pi gives the fraction of these which make some kind of collision in the lump before escaping. For each such collision a certain fraction yields additional fast neutrons thus, for each first-generation neutron 

---

The zeolite can easily be regenerated by heating. Similar high para selectivity can be achieved in the case of toluene by use of tert-butyl hypobromite as reagent with zeolite HX in a solvent mixture (CCI4 and ether). ZnBr2 supported on mesoporous silica or acid-activated montmorillonite is a fast, effective, reusable catalyst for the para-bromination of alkylbenzenes.257... 

Classical molecular dynamics simulations revealed in details the mechanism of the molecular decomposition for four selected molecules RDX, P HMX, DADNE and NQ. Parameters obtained from dynamic trajectories agree with the experimental characteristics h, describing the impact sensitivity and with calculated values of detonation energy for all investigated molecules. The parameters obtained from dynamics simulations could be used for fast effective testing of explosive materials. Anyway the method of testing based on dynamic simulations still needs to be worked out more preciously. That means ... 

The last type of common burette is the dispensing burette. It is easy to recognize by its size. It can carry up to one liter of liquid and is capable of fast, effective liquid dispensing. Its accuracy is about 0.5% of total volume. 

Anesthesia can be divided into three stages induction, maintenance, and recovery. Induction is defined as the period of time from onset of administration of the anesthetic to the development of effective surgical anesthesia in the patient. Maintenance provides a sustained surgical anesthesia. Recovery is the time from discontinuation of administration of anesthesia until consciousness is regained. Induction of anesthesia depends on how fast effective concentrations of the anesthetic drug reach the brain recovery is the reverse of induction and depends on how fast the anesthetic drug is removed from the brain. 

For the safety pharmacological assessment of candidate compounds to increase or reduce insulin resistance often long-term pre-treatment periods for 1 week or longer are necessary before an effect on insulin sensitivity can be detected. Candidate compounds causing an acute effect on lipolysis or andlipolysis of adipose tissue with subsequent changes in free fatty acids normally causes also a fast effect on peripheral insulin sensitivity, which can be measured after a relatively short (16h) pre-treatment period (Schoelch et al. 2004). 

The primary parameter AUCo-oo was subjected to an analysis of variance (ANOVA) including sequence, subject nested within sequence (subject (sequence)), period and treatment (non-fasting/fasting) effects. The sequence effect was tested using the subject (sequence) mean square from the ANOVA as an error term. All other main effects were tested against the residual error (error mean square) from the ANOVA. The ANOVA was performed on ln-transformed data. Lor ratios 90 % confidence intervals were constructed. The point estimates and confidence limits were calculated as antilogs and were expressed as percentages. The... 

Advantages. Retention time prediction is a fast, effective way to get an idea of the approximate retention time that can be expected for a given compound under a given set of conditions. 

Rgure 2.13 Postprandial and fasting effects on blood/gas partition coefficients (A) the broken line represents the situation in which the values of the two blood/gas partition coefficients are identical. 

Dye C.I. number Light-fastness effect on dyeing S.D.C. Test 3,... 

Important moment in reactivator s action on NMT is that most of them have strong and fast effect. In the same time reactivation of ChE can be a long lasting process. Electron microscopic histochemical investigation showed that reactivators of ChE recover a very small amount of AChE on postsynaptic membrane of neuromuscular junction [7],... 

The fast effective diffusion coefficient Dlcll is plotted as a function of polyelectrolyte concentration and it increases as C increases. From the logarithm plot a power law is deduced >feff varies as C045 0 05. 

In principle, liquid crystalline polymers can be applied in displays. Unfortunately, the response of them to the external fields isn t satisfactory because their viscosity is greater than the small molecular mass liquid crystals by a few orders of magnitude. In fact, only when the temperature is near the glass transition temperature, can the response be measured in seconds. Apparently, this is far from the real requirement. One may mix the liquid crystalline polymer with small molecular mass liquid crystal for such a purpose, but the mixture doesn t show an advantage over the small molecular mass liquid crystal displays. The ferroelectric liquid crystalline polymer is an exception. It works with a very fast effect and can achieve a display with a response time of a few milliseconds or a fewr tens of milliseconds. 

Choose the manipulation that has a direct and fast effect on a controlled variable. 

In rodents, preanalytical factors such as food intake and restraint may alter plasma ALT (see Chapter 12 also). A 50% food restriction over 210 days in rats resulted in elevated ALT values compared to controls (Schwartz, Tornaben, and Boxhill 1973), while reduced levels of ALT were observed in a study of fasting effects on the oral toxicity of several xenobiotics (Kast and Nishikawa 1981). Changes of ALT related to diet may reflect perturbations of gluconeogenesis (Toropila et al. 1996). There are now several examples where plasma ALT falls after the administration of xenobiotics due to effects on pyridoxal phosphate, which is a cofactor necessary for action of the aminotransferases AST and ALT (Dhami et al. 1979 Rhodes et al. 1987 Waner et al. 1990 Waner and Nyska 1991). Such effects may confuse the interpretation of data when hepatotoxicity occurs and tends to increase ALT, but where there is an opposing effect due to reductions in pyridoxal phosphate. Further complications with ALT have been described by Wells and To (1986) in covalent binding studies with acetaminophen. 

The reboiler duty Q2 has a strong and fast effect on all impurities (Figure 17.18b). The curves show two competing effects, stripping-out and accumulation through recycles. The first is faster at very short time, but is balanced by the second at longer times. The most important effect is on the impurity Ii, both dynamically and at steady-state. 

The membrane ion channels are the molecular targets for several toxins that induce fast effects in cells. The chemical structure ofYTX [5-7] resembles those of brevetoxins and ciguatoxins, with more than ten contiguous ether rings. These two groups of toxins are fast and potent activators of voltagegated sodium channels, therefore some interaction of YTX with cellular ion channels could be expected. However, YTX did not interact with sodium channels and did not induce any competitive displacement of brevetoxins from site five of sodium channels [8]. 

Acknowledgement. I thank Ms Joanne Cleghorn for fast, effective and resourceful assistance in obtaining literature. 

Recently, we have shown that the supramolecular approach (a non-covalent two-fold extra-ligation in conjunction with Zn-porphyrin chemical dimers and trimers) can be successfully employed to create a variety of multiporphyrin structures capable of the fast effective intra-complex energy migration and photoinduced electron transfer [5]. Following this self-assembly principle we have succeeded to anchor in pyridyl substituted porphyrin molecules on CdSe/ZnS QD surfaces. In this case, CdSe/ZnS QDs show luminescence quenching induced by dynamic and/or static interactions between QD and porphyrins depending critically on sample stability, temperature and solvent polarity [6]. The general focus of this contribution is devoted to demonstrate the... 

The Fast Effect. Though Szilard seems to have been the first to point out the importance of fast fission in uranium-238, Wigner and his group were the first to systematize the calculation, particularly the calculation of the first collision escape probability in various geometries. (Wigner made the latter calculation by first solving the diffusion equation, where the kernel is of the form e" /a , and then integrating with respect to a to get the transport kernel,. ... 

Szilard, also working at Columbia, became interested around this time in what is now called the fast effect. The fast effect, is the increase in the multiplication constant obtained by the emission of neutrons by which is induced to fission by the fission neutrons before they are slowed down. Szilard measured both the cross section of such fission neutrons to induce fast fission and also their inelastic cross section, i.e., the probability for their being slowed down below the fast fission threshold by an inelastic collision with uranium. He concluded on the basis of these measurements that one may obtain an increase of as much as 6-8% in the multiplication constant by using large and metallic lumps of uranium. Szilard was also somewhat discouraged by the low multiplication constant which Fermi s experiment gave but was far from giving up hope. 

The fast effect discovered a short time before by Szilard was omitted in these calculations and this proved to be a serious error, although we now know that the fast effect is less than half as great as Szilard calculated. I believed at that time that it is even smaller than that. The lattice which I proposed for the oxide proved later on to have a multiplication constant only about 2% higher than that of Fermi s Columbia lattice. The reason that it was so much smaller (about 3%) than I expected was mainly due to the fact that the fast effect was much smaller in it than in Fermi s lattice. However I did not quite believe in the fast effect and argued furthermore that if it existed we would recover the loss incurred by the transition to the smaller lattice when we replace the oxide by metal. 

Papers 29 and 30 served as the basis for the earhest calculations of the multiplication constant in an infinite heterogeneous reactor. By early 1942, the significance of fast fission was recognized, and all later calculations included estimates of e, the fast effect. This gave the four-factor formula, k = rjepf rj being the number of neutrons released per neutron absorbed in U. The quantity actually calculated in the following reports was rj = (1/ep/), k = r /rj ... 

There is no relevant difference between the fast effect in a finite and infinite lattice. However, the probability p that a neutron with an energy... 

In these and the above equations, the a are cross sections per imit volume, the a in (8) is scattering cross section, the average loss in r per collision. The are used because the material may contain different types of atoms. The (Ta is the thermal absorption cross section r(r) the resonance absorption cross section per unit volume. The = qef is the multiplication constant divided by the resonance escape probability. The product of thermal utilization / and (Ta is the effective cross section of uranium per unit volume, i.e., its cross section per unit volume multiplied by the thermal neutron density in it and divided by the average thermal neutron density. One can write, therefore, (Tu for f(Ta- If one multiplies this with rj the result is the same as crfU where fission cross section for thermal neutrons per unit volume, p the number of fast neutrons per fission. As a result, the third term in (7) can be written also as e is the multiplication by fast effect)... 

---