126 research outputs found
Analysis of optical magnetoelectric effect in GaFeO_3
We study the optical absorption spectra in a polar ferrimagnet GaFeO_3. We
consider the E1, E2 and M1 processes on Fe atoms. It is shown that the
magnetoelectric effect on the absorption spectra arises from the E1-M1
interference process through the hybridization between the 4p and 3d states in
the noncentrosymmetry environment of Fe atoms. We perform a microscopic
calculation of the spectra on a cluster model of FeO_6 consisting of an
octahedron of O atoms and an Fe atom displaced from the center with reasonable
values for Coulomb interaction and hybridization. We obtain the magnetoelectric
spectra, which depend on the direction of magnetization, as a function of
photon energy in the optical region 1.0-2.5 eV, in agreement with the
experiment.Comment: 18 pages, 5 figure
Hard Photodisintegration of a Proton Pair
We present a study of high energy photodisintegration of proton-pairs through the γ + 3He → p + p + n channel. Photon energies, Eγ , from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. The s−11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed for the first time. The onset of the scaling is at a higher energy and the cross section is significantly lower than for deuteron (pn pair) photodisintegration. For Eγ below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration
Heat-mode excitation in a proximity superconductor
Mesoscopic superconductivity deals with various quasiparticle excitation
modes, only one of them -- the charge-mode -- being directly accessible for
conductance measurements due to the imbalance in populations of quasi-electron
and quasi-hole excitation branches. Other modes carrying heat or even spin,
valley etc. currents populate the branches equally and are charge-neutral that
makes them much harder to control. This noticeable gap in the experimental
studies of mesoscopic non-equilibrium superconductivity can be filled by going
beyond the conventional DC transport measurements and exploiting spontaneous
current fluctuations. Here, we perform the first experiment of this kind and
investigate the transport of heat in an open hybrid device based on a
superconductor proximitized InAs nanowire. Using shot noise measurements we
observe a novel effect of sub-gap Andreev heat guiding along the
superconducting interface and fully characterize it in terms of the thermal
conductance on the order of , tunable by a back gate
voltage. Understanding of the heat-mode also uncovers its implicit signatures
in the non-local charge transport. Our experiments open a direct pathway to
probe generic neutral excitations in superconducting hybrids.Comment: revised, 20 pages with supplementa
Entropic force of polymers on a cone tip
We consider polymers attached to the tip of a cone, and the resulting force
due to entropy loss on approaching a plate (or another cone). At separations
shorter than the polymer radius of gyration R_g, the only relevant length scale
is the tip-plate (or tip-tip) separation h, and the entropic force is given by
F=A kT/h. The universal amplitude A can be related to (geometry dependent)
correlation exponents of long polymers. We compute A for phantom polymers, and
for self-avoiding (including star) polymers by epsilon-expansion, as well as by
numerical simulations in 3 dimensions
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High-Quality Graphene Using Boudouard Reaction
Following the game-changing high-pressure CO (HiPco) process that established the first facile route toward large-scale production of single-walled carbon nanotubes, CO synthesis of cm-sized graphene crystals of ultra-high purity grown during tens of minutes is proposed. The Boudouard reaction serves for the first time to produce individual monolayer structures on the surface of a metal catalyst, thereby providing a chemical vapor deposition technique free from molecular and atomic hydrogen as well as vacuum conditions. This approach facilitates inhibition of the graphene nucleation from the CO/CO2 mixture and maintains a high growth rate of graphene seeds reaching large-scale monocrystals. Unique features of the Boudouard reaction coupled with CO-driven catalyst engineering ensure not only suppression of the second layer growth but also provide a simple and reliable technique for surface cleaning. Aside from being a novel carbon source, carbon monoxide ensures peculiar modification of catalyst and in general opens avenues for breakthrough graphene-catalyst composite production
Hard Photodisintegration of a Proton Pair
We present a study of high energy photodisintegration of proton-pairs through
the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used
in kinematics corresponding to a proton pair with high relative momentum and a
neutron nearly at rest. The s-11 scaling of the cross section, as predicted by
the constituent counting rule for two nucleon photodisintegration, was observed
for the first time. The onset of the scaling is at a higher energy and the
cross section is significantly lower than for deuteron (pn pair)
photodisintegration. For photon energies below the scaling region, the scaled
cross section was found to present a strong energy-dependent structure not
observed in deuteron photodisintegration.Comment: 7 pages, 3 figures, for submission to Phys. Lett.
Recent physician strike in Israel: a health system under stress?
In 2011, a series of physician strikes in Israel followed eight months of unsuccessful negotiations with the government (Ministry of Health and the Ministry of Finance). Strikes by physicians may be a warning that all is not well in a health system and protestors have claimed that they signify a system failure. In contrast, others argue that strikes have been a feature of the Israeli health system from its inception and should not be a cause for alarm. This paper analyses the Israeli health system from the perspective of the strikers' demands using the World Health Organisation's six health system building blocks as a framework, including: service delivery; health workforce; information; medical products, vaccines and technologies; leadership and governance; and financing. While we recognise that the immediate causes of the 2011 strikes were concerns about salaries and working conditions, we argue that a complex set of interacting factors underlie the strikers' demands, resonating with issues relating to five of the WHO building blocks. We argue that of the five, three are most significant and limit progress with all the others: a disgruntled health workforce, many of whom believe that striking is the only way to be heard; a lack of leadership by the government in understanding and responding to physicians' concerns; and a purported information insufficiency, manifest as a lack of critique and analysis that may have prevented those at the top from making a reliable diagnosis of the system's problems. This paper argues that there are cracks within the Israeli health system but that these are not irresolvable. The Israeli health system is a relatively new and popular health system, but there are no grounds for complacency
Isoform-specific targeting of PKA to multivesicular bodies
PKA RIα subunit is localized to MVBs by the A-kinase–anchoring protein AKAP11 when disassociated from the PKA catalytic subunit
Identification of casein kinase 1, casein kinase 2, and cAMP-dependent protein kinase-like activities in Trypanosoma evansi
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