831 research outputs found
Bioenergetic Consequences of Lactose Starvation for Continuously Cultured Streptococcus cremoris
Подавление синхронной помехи в ЯКР с модуляцией Зеемана
Рассмотрены принципы частотной модуляции и модуляции Зеемана в ядерном квадрупольном резонансе и показаны преимущества последней. Предложен метод устранения синхронной помехи, вызываемой переключением магнитного поля. Приведены результаты наблюдения резонансной линии ¹⁴N с достоверной формой в образце гексаметилентетрамине массой 2 г.Розглянуто принципи частотної модуляції та модуляції Зеемана в ядерному квадрупольному резонансі та показано переваги останньої. Запропоновано метод усунення синхронної завади, спричиненої перемиканням магнітного поля. Наведено результат спостереження резонансної лінії ¹⁴N з достовірною формою у зразку гексаметилентетраміну масою 2 г.The principles of frequency and Zeeman modulation in nuclear quadrupole resonance were considered, and the advantages of the latter were shown. The authors propose a method to eliminate the synchronous noise caused by switching of the magnetic field. Results of observations of the resonance line with ¹⁴N in the hexamethylenetetramine sample weighing 2 g were given
Stresses in isostatic granular systems and emergence of force chains
Progress is reported on several questions that bedevil understanding of
granular systems: (i) are the stress equations elliptic, parabolic or
hyperbolic? (ii) how can the often-observed force chains be predicted from a
first-principles continuous theory? (iii) How to relate insight from isostatic
systems to general packings? Explicit equations are derived for the stress
components in two dimensions including the dependence on the local structure.
The equations are shown to be hyperbolic and their general solutions, as well
as the Green function, are found. It is shown that the solutions give rise to
force chains and the explicit dependence of the force chains trajectories and
magnitudes on the local geometry is predicted. Direct experimental tests of the
predictions are proposed. Finally, a framework is proposed to relate the
analysis to non-isostatic and more realistic granular assemblies.Comment: 4 pages, 2 figures, Corrected typos and clkearer text, submitted to
Phys. Rev. Let
A practical framework for tracing sources of Salmonella in a pig slaughter plant
Salmonella causes around 30 000 cases of human illness per year in The Netherlands, of which an estimated 25% is caused by pork. Salmonella carrying pigs and resident flora on slaughter equipment are relevant sources of carcass contamination. Although recognized, these sources from which and the routes through which Salmonella is transmitted to the pig carcasses during slaughter are not well understood in a quantitative way
Development of Stresses in Cohesionless Poured Sand
The pressure distribution beneath a conical sandpile, created by pouring sand
from a point source onto a rough rigid support, shows a pronounced minimum
below the apex (`the dip'). Recent work of the authors has attempted to explain
this phenomenon by invoking local rules for stress propagation that depend on
the local geometry, and hence on the construction history, of the medium. We
discuss the fundamental difference between such approaches, which lead to
hyperbolic differential equations, and elastoplastic models, for which the
equations are elliptic within any elastic zones present .... This displacement
field appears to be either ill-defined, or defined relative to a reference
state whose physical existence is in doubt. Insofar as their predictions depend
on physical factors unknown and outside experimental control, such
elastoplastic models predict that the observations should be intrinsically
irreproducible .... Our hyperbolic models are based instead on a physical
picture of the material, in which (a) the load is supported by a skeletal
network of force chains ("stress paths") whose geometry depends on construction
history; (b) this network is `fragile' or marginally stable, in a sense that we
define. .... We point out that our hyperbolic models can nonetheless be
reconciled with elastoplastic ideas by taking the limit of an extremely
anisotropic yield condition.Comment: 25 pages, latex RS.tex with rspublic.sty, 7 figures in Rsfig.ps.
Philosophical Transactions A, Royal Society, submitted 02/9
Static avalanches and Giant stress fluctuations in Silos
We propose a simple model for arch formation in silos. We show that small
pertubations (such as the thermal expansion of the beads) may lead to giant
stress fluctuations on the bottom plate of the silo. The relative amplitude
of these fluctuations are found to be power-law distributed, as
, . These fluctuations are related to large
scale `static avalanches', which correspond to long-range redistributions of
stress paths within the silo.Comment: 10 pages, 4 figures.p
Архітектурна спадщина Закарпаття під натиском новобуду
Multilocus sequence types (STs) were determined for 232 and 737 Campylobacter jejuni/coli isolates from Dutch travellers and domestically acquired cases, respectively. Putative risk factors for travel-related campylobacteriosis, and for domestically acquired campylobacteriosis caused by exotic STs (putatively carried by returning travellers), were investigated. Travelling to Asia, Africa, Latin America and the Caribbean, and Southern Europe significantly increased the risk of acquiring campylobacteriosis compared to travelling within Western Europe. Besides eating chicken, using antacids, and having chronic enteropathies, we identified eating vegetable salad outside Europe, drinking bottled water in high-risk destinations, and handling/eating undercooked pork as possible risk factors for travel-related campylobacteriosis. Factors associated with domestically acquired campylobacteriosis caused by exotic STs involved predominantly person-to-person contacts around popular holiday periods. We concluded that putative determinants of travel-related campylobacteriosis differ from those of domestically acquired infections and that returning travellers may carry several exotic strains that might subsequently spread to domestic populations even through limited person-to-person transmission
From casein to cheese: The role of Lactococcus lactis
Lactococci have limited biosynthetic abilities. In addition to the energy sources many solutes have to be taken up. Essential and non-essential amino acids are accumulated via specific transport systems. The concentration of these solutes in milk is insufficient to support optimal growth. Cells secrete proteinases and peptidases to hydrolyse casein. During milk fermentation, the growth requirements of lactococci are satisfied by the peptides and amino acids released upon casein degradation. When present in limiting amounts. amino acids are acquired by uptake and subsequent hydrolysis of peptides. The effects of an imbalance of the supply of amino acids on the growth and metsbolic activities of these bacteria are discussed
Prognostic significance of TP53 accumulation in human primary breast cancer: Comparison between a rapid quantitative immunoassay and SSCP analysis
Stress in frictionless granular material: Adaptive Network Simulations
We present a minimalistic approach to simulations of force transmission
through granular systems. We start from a configuration containing cohesive
(tensile) contact forces and use an adaptive procedure to find the stable
configuration with no tensile contact forces. The procedure works by
sequentially removing and adding individual contacts between adjacent beads,
while the bead positions are not modified. In a series of two-dimensional
realizations, the resulting force networks are shown to satisfy a linear
constraint among the three components of average stress, as anticipated by
recent theories. The coefficients in the linear constraint remain nearly
constant for a range of shear loadings up to about .6 of the normal loading.
The spatial distribution of contact forces shows strong concentration along
``force chains". The probability of contact forces of magnitude f shows an
exponential falloff with f. The response to a local perturbing force is
concentrated along two characteristic rays directed downward and laterally.Comment: 8 pages, 8 figure
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