7,481 research outputs found
Optimisation of the Photostimulated Luminescence (PSL) Tests to Detect Irradiated Dietary Supplements: Experimental Studies of Pre-Concentration, Depletion Rate Analysis and Multiwavelength PSL Analysis
No abstract available
Observed distribution functions of H, He, C, O, and Fe in corotating energetic particle streams: Implications for interplanetary acceleration and propagation
Distribution functions for H, He, C, O, and Fe derived from our IMP 8 measurements of approximately 0.15 to approximately 8 MeV/nucleon particles in three corotating streams observed near earth are shown to have a simple exponential dependence on the particle speed. The e-folding speed, v sub o, is typically 0.01c, is found to be the same for the distribution functions of all elements examined, and varies little from one corotating event to the next. The relative abundances of energetic particles in these events resemble most closely the solar coronal composition and, thus, presumably that of the solar wind. These results may imply that the acceleration of these particles, which occurs in corotating interaction regions at several AU from the sun, is by a statistical process
Pressure-induced ferromagnetism with strong Ising-type anisotropy in YbCuSi
We report dc magnetic measurements on YbCuSi at pressures above 10
GPa using a miniature ceramic anvil cell. YbCuSi shows a
pressure-induced transition from the non-magnetic to a magnetic phase at 8 GPa.
We find a spontaneous dc magnetization in the pressure-induced phase above 9.4
GPa. The pressure dependence of the ferromagnetic transition temperature T_C
and the spontaneous magnetic moment m_0 at 2.0 K have been determined. The
value of m_0 in the present macroscopic measurement is less than half of that
determined via Mossbauer experiment. The difference may be attributed to
spatial phase separation between the ferromagnetic and paramagnetic phases.
This separation suggests that the pressure-induced phase boundary between the
paramagnetic and ferromagnetic states is of first order. Further, we have
studied the magnetic anisotropy in the pressure-induced ferromagnetic state.
The effect of pressure on the magnetization with magnetic field along the
magnetic easy -axis is much larger than for field along the hard -axis in
the tetragonal structure. The pressure-induced phase has strong Ising-type
uniaxial anisotropy, consistent with the two crystal electric field (CEF)
models proposed for YbCuSi.Comment: 5 pages, 3 figure
Radio Frequency Tunable Oscillator Device Based on SmB6 Microcrystal
Radio frequency tunable oscillators are vital electronic components for
signal generation, characterization, and processing. They are often constructed
with a resonant circuit and a 'negative' resistor, such as a Gunn-diode,
involving complex structure and large footprints. Here we report that a piece
of SmB6, 100 micron in size, works as a current-controlled oscillator in the 30
MHz frequency range. SmB6 is a strongly correlated Kondo insulator that was
recently found to have a robust surface state likely to be protected by the
topology of its electronics structure. We exploit its non-linear dynamics, and
demonstrate large AC voltage outputs with frequencies from 20 Hz to 30 MHz by
adjusting a small DC bias current. The behaviors of these oscillators agree
well with a theoretical model describing the thermal and electronic dynamics of
coupled surface and bulk states. With reduced crystal size we anticipate the
device to work at higher frequencies, even in the THz regime. This type of
oscillator might be realized in other materials with a metallic surface and a
semiconducting bulk.Comment: v3 to appear in Physical Review Letter
Unconventional critical scaling of magnetization in uranium ferromagnetic superconductors UGe and URhGe
We report a dc magnetization study of the critical phenomenon around the
ferromagnetic transition temperature T_C in high-quality single crystals of
uranium ferromagnetic superconductors UGe2 and URhGe. The critical exponents,
beta for the temperature dependence of the magnetization below T_C, gamma for
the magnetic susceptibility, and delta for the magnetic isothermal at T_C have
been determined with a modified Arrott plot, a Kouvel-Fisher plot, and the
scaling analysis. Magnetization in the ferromagnetic state has strong uniaxial
magnetic anisotropy in the two compounds. However, the universality class of
the critical phenomena do not belong to the three dimensional (3D) Ising
system. Although the values of beta in UGe2 and URhGe are close to those in the
3D magnets, the values of gamma are close to unity, that expected from the mean
field theory. Similar critical exponents have been reported previously for the
3D Ising ferromagnet UIr where superconductivity appears under high pressure.
The critical behavior may be limited to a very narrow Ginzburg critical region
of 1 mK because of the strong itinerant character of the 5f electrons in the
ferromagnetic superconductor UCoGe where the mean field behavior of the
magnetization has been reported. The unconventional critical scaling of
magnetization in UGe2, URhGe and UIr cannot be explained via previous
approaches to critical phenomena. The ferromagnetic correlation between the 5f
electrons differs from that in the 3D Ising system and this difference may be a
key point for the understanding of the ferromagnetism where superconductivity
emerges.Comment: 8 pages, 5 figure
Strong Correlation between Anomalous Quasiparticle Scattering and Unconventional Superconductivity in Hidden Order Phase of URuSi
The pressure dependent electrical resistivity of URuSi has been
studied at high pressure across the first order phase boundary of where
the ground state switches under pressure from "hidden order" (HO) to large
moment antiferromagnetic (LAFM) states. The electrical transport in
URuSi at low temperatures shows a strong sample dependence. We have
measured an ultra-clean single crystal whose quality is the highest among those
used in previous studies. The generalized power law
analysis finds that the electric
transport property deviates from Fermi liquid theory in the HO phase but obeys
the theory well above . The analysis using the polynomial in
expression
reveals the relation in the HO
phase. While the pressure dependence of is very weak,
is roughly proportional to . This suggests a strong
correlation between the anomalous quasiparticle scattering and the
superconductivity and that both have a common origin. The present study
clarifies a universality of the HO phase inherent in strongly correlated
electron superconductors near quantum criticality
Examining the Relationship Between Self-Efficacy and Health Behaviors Among College Students
Adolescents’ transition into adulthood often coincides with significant developmental change processes. Behavioral patterns established during this period can determine risk and quality of life trajectories (Ben-Shlomo & Kuh, 2002, Halfon & Hochstein, 2002). Social support facilitates health behavior change and college students have ready access to peers with shared goals. In addition to social support, self-efficacy has also been associated with student health as a protective and predictive factor of healthy behaviors (Von Ah, Ebert, Ngamvitroj, Park, & Kang, 2004). Research indicates a strong relationship between self-efficacy and health behaviors; however, the direction of causality is unclear and there is little understanding of how self-efficacy changes. The current experiment examined the effects of observational learning/modeling and social support created through course-related, small groups or Accountability Teams (ATs) on individual self-efficacy and physical activity. The primary hypothesis was that individual health self-efficacy of students would interact with types of ATs, affecting students’ general self-efficacy, perception of health, and physical activity.
Participants in this experiment were undergraduate students enrolled in a lifelong fitness health course. Self-report measures of health self-efficacy (HSE), general self-efficacy, quality of life, and general health were distributed and completed by participants. Additionally, students submitted measurements of body fat percentage and physical activity (e.g., number of steps taken). Participants were assigned to support groups called “Accountability Teams” within their respective health class. Teams were assigned based on students’ HSE; each group consisted of either matched HSE (i.e., all students were low or high HSE) or mixed health self-efficacy (i.e., students in the AT were a mix of low and high HSE). The results indicate interactions in which students of Hi/Lo HSE respond differently in ATs. Overall, results suggest that LoHSE students placed in matched (homogenous) HSE groups had the best outcomes on multiple dimensions of health and health behaviors, followed by HiHSE students in mixed HSE groups. HiHSE students in matched groups has poor outcomes. The poorest outcomes were for LoHSE students in the mixed AT condition. These results are discussed within a self-efficacy frame and implications for behavioral health courses and therapy are discussed
Severe Fermi Surface Reconstruction at a Metamagnetic-Transition in CaSrRuO (for )
We report an electrical transport study in CaSrRuO single
crystals at high magnetic fields (). For , the Hall constant
decreases sharply at an anisotropic metamagnetic (MM) transition
reaching its value for SrRuO at high fields. A sharp decrease in the
coefficient of the resistivity -term and a change in the structure of
the angular magnetoresistance oscillations (AMRO) for rotating in the
planes, confirms the reconstruction of the Fermi surface (FS). Our observations
and LDA calculations indicate a strong dependence of the FS on the Ca
concentration and suggest the coexistence of itinerant and localized electronic
states in single layered ruthenates.Comment: 5 pages, 4 fig
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