7,330 research outputs found
Increases in the Irreversibility Field and the Upper Critical Field of Bulk MgB2 by ZrB2 Addition
In a study of the influence of ZrB2 additions on the irreversibility field,
Birr and the upper critical field Bc2, bulk samples with 7.5 at. % ZrB2
additions were made by a powder milling and compaction technique. These samples
were then heated to 700-900C for 0.5 hours. Resistive transitions were measured
at 4.2 K and Birr and Bc2 values were determined. An increase in Bc2 from 20.5
T to 28.6 T and enhancement of Birr from 16 T to 24 T were observed in the ZrB2
doped sample as compared to the binary sample at 4.2 K. Critical field
increases similar to those found with SiC doping were seen at 4.2 K. At higher
temperatures, increases in Birr were also determined by M-H loop extrapolation
and closure. Values of Birr which were enhanced with ZrB2 doping (as compared
to the binary) were seen at temperatures up to 34 K, with Birr values larger
than those for SiC doped samples at higher temperatures. The transition
temperature, Tc, was then measured using DC susceptibility and a 2.5 K drop of
the midpoint of Tc was observed. The critical current density was determined
using magnetic measurements and was found to increase at all temperatures
between 4.2 K and 35 K with ZrB2 doping.Comment: 15 pages, 5 figs, 1 tabl
Beyond the standard entropic inequalities: stronger scalar separability criteria and their applications
Recently it was shown that if a given state fulfils the reduction criterion
it must also satisfy the known entropic inequalities. Now the questions arises
whether on the assumption that stronger criteria based on positive but not
completely positive maps are satisfied, it is possible to derive some scalar
inequalities stronger than the entropic ones. In this paper we show that under
some assumptions the extended reduction criterion [H.-P. Breuer, Phys. Rev.
Lett 97, 080501 (2006); W. Hall, J. Phys. A 40, 6183 (2007)] leads to some
entropic--like inequalities which are much stronger than their entropic
counterparts. The comparison of the derived inequalities with other
separability criteria shows that such approach might lead to strong scalar
criteria detecting both distillable and bound entanglement. In particular, in
the case of SO(3)-invariant states it is shown that the present inequalities
detect entanglement in regions in which entanglement witnesses based on
extended reduction map fail. It should be also emphasized that in the case of
states the derived inequalities detect entanglement efficiently,
while the extended reduction maps are useless when acting on the qubit
subsystem. Moreover, there is a natural way to construct a many-copy
entanglement witnesses based on the derived inequalities so, in principle,
there is a possibility of experimental realization. Some open problems and
possibilities for further studies are outlined.Comment: 15 Pages, RevTex, 7 figures, some new results were added, few
references changed, typos correcte
Slower-than-Light Spin-1/2 Particles Endowed with Negative Mass Squared
Extending in a straightforward way the standard Dirac theory, we study a
quantum mechanical wave-equation describing free spinning particles --which we
propose to call "Pseudotachyons" (PT's)-- which behave like tachyons in the
momentum space, but like subluminal particles (v<c) in the ordinary space. This
is allowed since, as it happens in every quantum theory for spin-1/2 particles,
the momentum operator (that is conserved) and the velocity operator (that is
not) are independent operators, which refer to independent quantities. As a
consequence, at variance with ordinary Dirac particles, for PT's the average
velocity is not equal to the classical velocity, but actually to the velocity
"dual" of the classical velocity. The speed of PT's is therefore smaller than
the speed of light. Since a lot of experimental data seems to involve a
negative mass squared for neutrinos, we suggest that these particles might be
PT's, travelling, because of their very small mass, at subluminal speeds very
close to c. The present theory is shown to be separately invariant under the C,
P, T transformations; the covariance under Lorentz transformations is also
proved. Furthermore, we derive the kinematical constraints linking 4-impulse,
4-velocity and 4-polarization of free PT'sComment: LaTeX; 20 page
Transport and magnetic Jc of MgB2 strands and small helical coils
The critical current densities of MgB2 monofilamentary strands with and
without SiC additions were measured at 4.2 K. Additionally, magnetic Jc at B =
1 T was measured from 4.2 K to 40 K. Various heat treatment times and
temperatures were investigated for both short samples and small helical coils.
SiC additions were seen to improve high field transport Jc at 4.2 K, but
improvements were not evident at 1 T at any temperature. Transport results were
relatively insensitive to heat treatment times and temperatures for both short
samples and coils in the 700C to 900C range.Comment: 8 text pages, 1 table, 4 fig
Atomic Data and Spectral Line Intensities for NI XVII
Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ni XVII. We include in the calculations the 23 lowest configurations, corresponding to 159 fine-structure levels: 3l3l', 3l4l0'' , and 3s5l0''' , with l,l' = s,p,d, l'' = s,p,d, f, and l''' = s,p,d. Collision strengths are calculated at five incident energies for all transitions at varying energies above the threshold of each transition. One additional energy, very close to the threshold of each transition, has also been included. Calculations have been carried out using the Flexible Atomic Code in the distorted wave approximation. Additional calculations have been performed with the University College London suite of codes for comparison. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8) - 10(exp 14) / cubic cm and at an electron temperature of logT(sub e)e(K) = 6.5, corresponding to the maximum abundance of Ni XVII. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI databas
Extensions of Lieb's concavity theorem
The operator function (A,B)\to\tr f(A,B)(K^*)K, defined on pairs of bounded
self-adjoint operators in the domain of a function f of two real variables, is
convex for every Hilbert Schmidt operator K, if and only if f is operator
convex. As a special case we obtain a new proof of Lieb's concavity theorem for
the function (A,B)\to\tr A^pK^*B^{q}K, where p and q are non-negative numbers
with sum p+q\le 1. In addition, we prove concavity of the operator function
(A,B)\to \tr(A(A+\mu_1)^{-1}K^* B(B+\mu_2)^{-1}K) on its natural domain
D_2(\mu_1,\mu_2), cf. Definition 4.1Comment: The format of one reference is changed such that CiteBase can
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Big brother is watching - using digital disease surveillance tools for near real-time forecasting
Abstract for the International Journal of Infectious Diseases 79 (S1) (2019).https://www.ijidonline.com/article/S1201-9712(18)34659-9/abstractPublished versio
Tardive syndromes
Dopamine receptor-blocking antipsychotics, first introduced into clinical practice in 1952, were hailed as a panacea in the treatment of a number of psychiatric disorders. However, within 5Â years, this notion was to be shattered by the recognition of both acute and chronic drug-induced movement disorders which can accompany their administration. Tardive syndromes, denoting the delayed onset of movement disorders following administration of dopamine receptor-blocking (and also other) drugs, have diverse manifestations ranging from the classic oro-bucco-lingual dyskinesia, through dystonic craniocervical and trunk posturing, to abnormal breathing patterns. Although tardive syndromes have been an important part of movement disorder clinical practice for over 60Â years, their pathophysiologic basis remains poorly understood and the optimal treatment approach remains unclear. This review summarises the current knowledge relating to these syndromes and provides clinicians with pragmatic, clinically focused guidance to their management
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