4,801 research outputs found
Effects of X-ray irradiation on human spermatogenesis
Direct cell kill and inhibition of mitosis have been suggested as mechanisms to explain the occurrence of absolute sterility following the irradiation of the testes. In order to obtain information on the existence and dose dependency of the mechanisms for man, a controlled study was initiated. Sixty-four men received a single midorgan dose to both of their testes ranging from 7.5 to 400r (f = .95). It was deduced from resulting pre-sterile period and sterile period data that both cell kill and mitosis halting mechanisms were operating. The maximum observed sterile period was 501 days with eventual recovery observed in each individual where the follow-up was complete. Thus man appears to be highly radiosensitive in regard to temporary sterility but quite radioresistant in regard to permanent sterility
Platyceroidini, a new tribe of North American stag beetles(Coleoptera: Lucanidae: Lucaninae)
The tribe Platyceroidini is created to accommodate two genera of North American stag beetles, Platyceroides Benesh and Platyceropsis Benesh (Lucanidae: Lucaninae). These genera are removed from the tribe Platycerini Mulsant
DFT Calculations as a Tool to Analyse Quadrupole Splittings of Spin Crossover Fe(II) complexes
Density functional methods have been applied to calculate the quadrupole
splitting of a series of iron(II) spin crossover complexes. Experimental and
calculated values are in reasonable agreement. In one case spin-orbit coupling
is necessary to explain the very small quadrupole splitting value of 0.77 mm/s
at 293 K for a high-spin isomer
An automated and versatile ultra-low temperature SQUID magnetometer
We present the design and construction of a SQUID-based magnetometer for
operation down to temperatures T = 10 mK, while retaining the compatibility
with the sample holders typically used in commercial SQUID magnetometers. The
system is based on a dc-SQUID coupled to a second-order gradiometer. The sample
is placed inside the plastic mixing chamber of a dilution refrigerator and is
thermalized directly by the 3He flow. The movement though the pickup coils is
obtained by lifting the whole dilution refrigerator insert. A home-developed
software provides full automation and an easy user interface.Comment: RevTex, 10 pages, 10 eps figures. High-resolution figures available
upon reques
Viscous to Inertial Crossover in Liquid Drop Coalescence
Using an electrical method and high-speed imaging we probe drop coalescence
down to 10 ns after the drops touch. By varying the liquid viscosity over two
decades, we conclude that at sufficiently low approach velocity where
deformation is not present, the drops coalesce with an unexpectedly late
crossover time between a regime dominated by viscous and one dominated by
inertial effects. We argue that the late crossover, not accounted for in the
theory, can be explained by an appropriate choice of length-scales present in
the flow geometry.Comment: 4 pages, 4 figure
Multiple transient memories in sheared suspensions: robustness, structure, and routes to plasticity
Multiple transient memories, originally discovered in charge-density-wave
conductors, are a remarkable and initially counterintuitive example of how a
system can store information about its driving. In this class of memories, a
system can learn multiple driving inputs, nearly all of which are eventually
forgotten despite their continual input. If sufficient noise is present, the
system regains plasticity so that it can continue to learn new memories
indefinitely. Recently, Keim & Nagel showed how multiple transient memories
could be generalized to a generic driven disordered system with noise, giving
as an example simulations of a simple model of a sheared non-Brownian
suspension. Here, we further explore simulation models of suspensions under
cyclic shear, focussing on three main themes: robustness, structure, and
overdriving. We show that multiple transient memories are a robust feature
independent of many details of the model. The steady-state spatial distribution
of the particles is sensitive to the driving algorithm; nonetheless, the memory
formation is independent of such a change in particle correlations. Finally, we
demonstrate that overdriving provides another means for controlling memory
formation and retention
Multiple transient memories in experiments on sheared non-Brownian suspensions
A system with multiple transient memories can remember a set of inputs but
subsequently forgets almost all of them, even as they are continually applied.
If noise is added, the system can store all memories indefinitely. The
phenomenon has recently been predicted for cyclically sheared non-Brownian
suspensions. Here we present experiments on such suspensions, finding behavior
consistent with multiple transient memories and showing how memories can be
stabilized by noise.Comment: 5 pages, 4 figure
Unconventional antiferromagnetic correlations of the doped Haldane gap system YBaNiZnO
We make a new proposal to describe the very low temperature susceptibility of
the doped Haldane gap compound YBaNiZnO. We propose a new
mean field model relevant for this compound. The ground state of this mean
field model is unconventional because antiferromagnetism coexists with random
dimers. We present new susceptibility experiments at very low temperature. We
obtain a Curie-Weiss susceptibility as expected
for antiferromagnetic correlations but we do not obtain a direct signature of
antiferromagnetic long range order. We explain how to obtain the ``impurity''
susceptibility by subtracting the Haldane gap contribution to
the total susceptibility. In the temperature range [1 K, 300 K] the
experimental data are well fitted by . In the temperature range [100 mK, 1 K] the experimental data are
well fitted by , where increases with
. This fit suggests the existence of a finite N\'eel temperature which is
however too small to be probed directly in our experiments. We also obtain a
maximum in the temperature dependence of the ac-susceptibility which
suggests the existence of antiferromagnetic correlations at very low
temperature.Comment: 19 pages, 17 figures, revised version (minor modifications
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