967 research outputs found
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means
of magnetization measurements in the temperature range between 1.95 K and Tc,
in an external magnetic field up to 9 T. Flux jumps were found in the
temperature range 1.95 K - 6 K, with the external magnetic field parallel to
the c axis of the investigated sample. The effect of sample history on magnetic
flux jumping was studied and it was found to be well accounted for by the
available theoretical models. The magnetic field sweep rate strongly influences
the flux jumping and this effect was interpreted in terms of the influence of
both flux creep and the thermal environment of the sample. Strong flux creep
was found in the temperature and magnetic field range where flux jumps occur
suggesting a relationship between the two. The heat exchange conditions between
the sample and the experimental environment also influence the flux jumping
behavior. Both these effects stabilize the sample against flux instabilities,
and this stabilizing effect increases with decreasing magnetic field sweep
rate. Demagnetizing effects are also shown to have a significant influence on
flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
Absence of Edge Localized Moments in the Doped Spin-Peierls System CuGeSiO
We report the observation of nuclear quadrupole resonance (NQR) of Cu from
the sites near the doping center in the spin-Peierls system
CuGeSiO. The signal appears as the satellites in the Cu NQR
spectrum, and has a suppressed nuclear spin-lattice relaxation rate indicative
of a singlet correlation rather than an enhanced magnetic correlation near the
doping center. Signal loss of Cu nuclei with no neighboring Si is also
observed. We conclude from these observations that the doping-induced moments
are not in the vicinity of the doping center but rather away from it.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
The effect of distributed exchange parameters on magnetocaloric refrigeration capacity in amorphous and nanocomposite materials
The temperature dependent magnetization of nanocomposite alloys has been fit with a modified Handrich-Kobe equation with an asymmetric exchange fluctuation parameter combined with the Arrott-Noakes equation. The two equations of state are combined to calculate the entropy change in the magnetocaloric effect associated with the ferromagnetic to paramagnetic phase transformation. The complete fit for the M(T) of (Fe70Ni30)88Zr7B4Cu nanocomposite powder is accomplished by combining the two theories. We investigate the broadening of the second-order transition arising from asymmetric exchange parameters and resulting from the fluctuations of interatomic spacing found in an amorphous matrix and the asymmetric dependence of exchange energy on interatomic spacing. The magnetic entropy curve revealed extra broadening with a refrigeration capacity (RC) value of 135 J/kg at 5 T, which is comparable to (Fe76Cr8-xMoxCu1B15) ribbons, which have a RC value of 180 J/kg for the same applied field. Broadening of the magnetic entropy can lead to larger RC values and a wider working temperature range, making nanocomposite alloys promising for magnetocaloric applications
Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments
We present an experimental study of thermally activated flux creep in a
superconducting ring-shaped epitaxial YBCO film as well as a new way of
analyzing the experimental data. The measurements were made in a wide range of
temperatures between 10 and 83 K. The upper temperature limit was dictated by
our experimental technique and at low temperatures we were limited by a
crossover to quantum tunneling of vortices. It is shown that the experimental
data can very well be described by assuming a simple thermally activated
hopping of vortices or vortex bundles over potential barriers, whereby the
hopping flux objects remain the same for all currents and temperatures. The new
procedure of data analysis also allows to establish the current and temperature
dependencies of the flux-creep activation energy U, as well as the temperature
dependence of the critical current Ic, from the flux-creep rates measured at
different temperatures. The variation of the activation energy with current,
U(I/Ic), is then used to reconstruct the profile of the potential barriers in
real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review
Impact of Two Types of Fitness Programs on Soldier Physical Fitness
International Journal of Exercise Science 15(4): 1326-1346, 2022. This study compared an expert supervised, fully resourced physical training (PT) program compared to a traditional physical training PT plan on Army Officer Candidate School (OSC) soldier fitness outcomes. This retrospective cohort study compared 228 OCS soldiers (179 male [26.74±3.78 years] and 49 female [26.55±4.18 years]) in two companies for 12 weeks. One company participated in a fully resourced PT program designed by fitness experts to improve overall fitness and mobility (TAP-C). One company participated in traditional physical training designed to excel on the Army combat fitness test (ACFT, includes deadlift, power throw, push up, sprint-drag-carry, core strength, run) developed and led by OCS soldiers with standard resources. We assessed performance on the ACFT events, and grip strength, standing broad jump, overhead squat, and 90/90 switch assessment. Analysis of covariance was used to compare main effects of company on ACFT measures, controlling for covariates of pretest score differences and sex. Results included a significant effect of group on ACFT performance (N=228), F(1, 223) = 12.8, p\u3c0.001 and on performance of five of the six ACFT events: MDL, F(1, 223) = 5.44, p = 0.021; HRP, F(1, 223) = 11.67, p \u3c 0.001; SDC, F(1, 223) = 20.06, p \u3c 0.001; LTK, F(1, 223) = 16.95, p \u3c 0.001; and 2MR, F(1, 223) = 23.76, p \u3c 0.001. The traditional company performed significantly better on ACFT muscular, anerobic and aerobic endurance focused events; the TAP-C company performed significantly better on muscular strength/explosive power events and mobility assessments
Central peak position in magnetization loops of high- superconductors
Exact analytical results are obtained for the magnetization of a
superconducting thin strip with a general behavior J_c(B) of the critical
current density. We show that within the critical-state model the magnetization
as function of applied field, B_a, has an extremum located exactly at B_a=0.
This result is in excellent agreement with presented experimental data for a
YBCO thin film. After introducing granularity by patterning the film, the
central peak becomes shifted to positive fields on the descending field branch
of the loop. Our results show that a positive peak position is a definite
signature of granularity in superconductors.Comment: $ pages, 6 figure
Cu Nuclear Quadrupole Resonance Study of the Spin-Peierls Compound Cu1-xMgxGeO3: A Possibility of Precursory Dimerization
We report on a zero-field 63Cu nuclear quadrupole resonance (NQR) study of
nonmagnetic Mg impurity substituted Cu1-xMgxGeO3 (single crystals; the
spin-Peierls transition temperature Tsp~14, 13.5, and 11 K for x=0, 0.0043, and
0.020) in a temperature range from 4.2 K to 250 K. We found that below T*~77 K,
Cu NQR spectra are broadened and nonexponential Cu nuclear spin-lattice
relaxation increases for undoped and more remarkably for Mg-doped samples. The
results indicate that random lattice distortion and impurity-induced spins
appear below T*, which we associate with a precursor of the spin-Peierls
transition. Conventional magnetic critical slowing down does not appear down to
4.2 K below Tsp.Comment: 4 pages, 4 figure
Discovery and Characterization of the Cryptic Psi Subunit of the Pseudomonad DNA Replicase
We previously reconstituted a minimal DNA replicase from Pseudomonas aeruginosa consisting of α and ϵ (polymerase and editing nuclease), β (processivity factor), and the essential τ, δ, and δ′ components of the clamp loader complex (Jarvis, T., Beaudry, A., Bullard, J., Janjic, N., and McHenry, C. (2005) J. Biol. Chem. 280, 7890-7900). In Escherichia coli DNA polymerase III holoenzyme, χ and Ψ are tightly associated clamp loader accessory subunits. The addition of E. coli χΨ to the minimal P. aeruginosa replicase stimulated its activity, suggesting the existence of χ and Ψ counterparts in P. aeruginosa. The P. aeruginosa χ subunit was recognizable from sequence similarity, but Ψ was not. Here we report purification of an endogenous replication complex from P. aeruginosa. Identification of the components led to the discovery of the cryptic Ψ subunit, encoded by holD. P. aeruginosa χ and Ψ were co-expressed and purified as a 1:1 complex. P. aeruginosa χΨ increased the specific activity of τ3δδ′ 25-fold and enabled the holoenzyme to function under physiological salt conditions. A synergistic effect between χΨ and single-stranded DNA binding protein was observed. Sequence similarity to P. aeruginosa Ψ allowed us to identify Ψ subunits from several other Pseudomonads and to predict probable translational start sites for this protein family. This represents the first identification of a highly divergent branch of the Ψ family and confirms the existence of Ψ in several organisms in which Ψ was not identifiable based on sequence similarity alone
Steering chiral swimmers along noisy helical paths
Chemotaxis along helical paths towards a target releasing a chemoattractant
is found in sperm cells and many microorganisms. We discuss the stochastic
differential geometry of the noisy helical swimming path of a chiral swimmer. A
chiral swimmer equipped with a simple feedback system can navigate in a
concentration gradient of chemoattractant. We derive an effective equation for
the alignment of helical paths with a concentration gradient which is related
to the alignment of a dipole in an external field. We discuss the chemotaxis
index in the presence of fluctuations.Comment: 8 pages, 1 figur
Spin Dynamics near the Superconductor-to-Insulator Transition in Impurity-Doped YBa2Cu4O8
We studied low-frequency spin dynamics near the impurity-induced
superconductor-to-insulator transition for underdoped high-Tc superconductor
YBa2(Cu1-xMx)4O8 (M=Ni, Zn) using the Cu nuclear quadrupole resonance (NQR)
spin-echo technique. We observed remarkable suppression of the normal-state
pseudo spin-gap and a loss of Cu NQR spectrum intensity at low temperatures
around the critical impurity concentration.Comment: 6 pages, 4 figures. To be published in J. Phys. Soc. Jpn. Vol.70,
No.7 (2001
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