27,166 research outputs found
Optimal Conditions for Kinetic Study of Succinate Dehydrogenase in Rat Liver
Succinate dehydrogenase (SDH) commonly is assayed as a marker enzyme for mitochondrial activity. The literature presents numerous conditions for conducting this assay due to the fact that, it has been difficult to get sufficient reduction of the acceptor dye, 2,3,5-triphenyl-2H-tetrazolium chloride (TTC). This study was undertaken to optimize the SDH-catalyzed reduction of TTC dye by evaluation of a greater range of molor ratios of TTC to succinate and by further evaluation of additives reported as beneficial. Improvement in enzyme specific activity was achieved by liver perfusion via the left cardiac ventricle with homogenizing solution. Increase in TTC from 1 to 10 mM and further increase to 20 mM resulted in major improvement in color production. The greatest improvement in apparent activity was achieved by addition of 1 mM phenozine methosulfate, a hydrogen transfer mediator. Use of CaCI₂. EDTA, Triton X-100, NaN₃ and KCN was not beneficial. The above modifications of the SDH assay resulted in greater sensitivity, the conduct of a greater number of assays with less tissue and the sacrifice of fewer animals
Contrasts between Equilibrium and Non-equilibrium Steady States: Computer Aided Discoveries in Simple Lattice Gases
A century ago, the foundations of equilibrium statistical mechanics were
laid. For a system in equilibrium with a thermal bath, much is understood
through the Boltzmann factor, exp{-H[C]/kT}, for the probability of finding the
system in any microscopic configuration C. In contrast, apart from some special
cases, little is known about the corresponding probabilities, if the same
system is in contact with more than one reservoir of energy, so that, even in
stationary states, there is a constant energy flux through our system. These
non-equilibrium steady states display many surprising properties. In
particular, even the simplest generalization of the Ising model offers a wealth
of unexpected phenomena. Mostly discovered through Monte Carlo simulations,
some of the novel properties are understood while many remain unexplained. A
brief review and some recent results will be presented, highlighting the sharp
contrasts between the equilibrium Ising system and this non-equilibrium
counterpart.Comment: 9 pages, 3 figure
Ethnic parity in labour market outcomes for benefit claimants
A significant gap exists in the UK between the employment rate for Ethnic Minorities and that for
Whites. From a policy perspective, it is important to know whether this gap is due to differences in
the characteristics of White and Ethnic Minority groups (which reduce the employability of Ethnic
Minority groups relative to Whites) or whether it results from some form of discriminatory behaviour
in the labour market. In this paper, we use administrative data to estimate ethnic differences in
employment and benefit receipt amongst individuals who began claiming a Jobcentre Plus benefit
in 2003. In contrast to much of the previous UK literature, we use a number of different quantitative
techniques to estimate this gap, and show that in a lot of cases the estimates obtained are very
sensitive to the techniques used. We argue that for the questions we are interested in and the data
we have, propensity score matching methods are the most robust approach to estimating ethnic
parity. We compare this preferred approach with estimates derived using alternative approaches
commonly used in the literature (generally regression-based techniques) to determine the extent to
which more straightforward methods are able to replicate those produced by matching. In many
cases, it turns out not to be possible to calculate satisfactory quantitative estimates even with
matching techniques: the characteristics of Whites and Ethnic Minorities are simply too different
before the Jobcentre Plus intervention to reliably estimate the parameters of interest. Moreover, for
a number of the groups, results seem to be very sensitive to the methodology used. This calls into
question previous results based on simple regression techniques, which are likely to hide the fact
that observationally different ethnic groups are de facto being compared on the basis of parametric
extrapolations. Two groups for which it was possible to calculate reasonably reliable results are
incapacity benefit (IB) and income support (IS). For these groups we find that large and significant
raw penalties almost always disappear once we appropriately control for pre-inflow background
and labour market characteristics. There is also a good degree of consistency across
methodologies
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Solid Freeform Fabrication of Artificial Human Teeth
In this paper, we describe a solid freeform fabrication procedure for human dental
restoration via porcelain slurry micro-extrusion. Based on submicron-sized dental porcelain
powder obtained via ball milling process, a porcelain slurry formulation has been developed. The
formulation developed allows the porcelain slurry to show a pseudoplastic behavior and
moderate viscosity, which permits the slurry to re-shape to form a near rectangular cross section.
A well-controlled cross-section geometry of the extrudate is important for micro-extrusion to
obtain uniform 2-D planes and for the addition of the sequential layers to form a 3-D object.
Human teeth are restored by this method directly from CAD digital models. After sintering,
shrinkage of the artificial teeth is uniform in all directions. Microstructure of the sintered teeth is
identical to that made via traditional dental restoration processes.Mechanical Engineerin
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Laser Densification of Extruded Dental Porcelain Bodies in Multi-Material Laser Densification (MMLD) Process
In this study commercial dental porcelain powder was deposited via slurry extrusion and
laser densified to fabricate dental restorations in a Multi-Material Laser Densification (MMLD)
process. The processing conditions for laser densification of single lines and closed rings were
investigated in order to avoid warping and cracking. Multi-layer rings were also investigated to
study the dependence of bonding between layers on the laser densification conditions. The laser
densified rings showed no warping, and good bonding between layers could be achieved when
the laser densification condition was selected properly. The mechanism to achieve porcelain
rings without warping and cracking is discussed. The understanding developed will pave the way
for fabricating a physical dental restoration unit.Mechanical Engineerin
Laser Interferometer Gravitational-Wave Observatory beam tube component and module leak testing
Laser Interferometer Gravitational-Wave Observatory (LIGO) is a joint project of the California Institute of Technology and the Massachusetts Institute of Technology funded by the National Science Foundation. The project is designed to detect gravitational waves from astrophysical sources such as supernova and black holes. The LIGO project constructed observatories at two sites in the U.S. Each site includes two beam tubes (each 4 km long) joined to form an "L" shape. The beam tube is a 1.25 m diam 304 L stainless steel, ultrahigh vacuum tube that will operate at 1×10^–9 Torr or better. The beam tube was manufactured using a custom spiral weld tube mill from material processed to reduce the outgassing rate in order to minimize pumping costs. The integrity of the beam tube was assured by helium mass spectrometer leak testing each component of the beam tube system prior to installation. Each 2 km long, isolatable beam tube module was then leak tested after completion
Two-Channel Totally Asymmetric Simple Exclusion Processes
Totally asymmetric simple exclusion processes, consisting of two coupled
parallel lattice chains with particles interacting with hard-core exclusion and
moving along the channels and between them, are considered. In the limit of
strong coupling between the channels, the particle currents, density profiles
and a phase diagram are calculated exactly by mapping the system into an
effective one-channel totally asymmetric exclusion model. For intermediate
couplings, a simple approximate theory, that describes the particle dynamics in
vertical clusters of two corresponding parallel sites exactly and neglects the
correlations between different vertical clusters, is developed. It is found
that, similarly to the case of one-channel totally asymmetric simple exclusion
processes, there are three stationary state phases, although the phase
boundaries and stationary properties strongly depend on inter-channel coupling.
An extensive computer Monte Carlo simulations fully support the theoretical
predictions.Comment: 13 pages, 10 figure
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