9,444 research outputs found

    Preference Erosion and Multilateral Trade Liberalization

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    Because of concern that OECD tariff reductions will translate into worsening export performance for the least developed countries, trade preferences have proven a stumbling block to developing country support for multilateral liberalization. We examine the actual scope for preference erosion, including an econometric assessment of the actual utilization, and also the scope for erosion estimated by modeling full elimination of OECD tariffs and hence full MFN liberalization-based preference erosion. Preferences are underutilized due to administrative burden‚ÄĒestimated to be at least 4 percent on average‚ÄĒreducing the magnitude of erosion costs significantly. For those products where preferences are used (are of value), the primary negative impact follows from erosion of EU preferences. This suggests the erosion problem is primarily bilateral rather than a WTO-based concern.preference erosion, GSP, WTO, Doha Round, trade and development

    Transport in the metallic regime of Mn doped III-V Semiconductors

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    The standard model of Mn doping in GaAs is subjected to a coherent potential approximation (CPA) treatment. Transport coefficients are evaluated within the linear response Kubo formalism. Both normal (NHE) and anomalous contributions (AHE) to the Hall effect are examined. We use a simple model density of states to describe the undoped valence band. The CPA bandstructure evolves into a spin split band caused by the p‚ąídp-d exchange scattering with Mn dopants. This gives rise to a strong magnetoresistance, which decreases sharply with temperature. The temperature (TT) dependence of the resistance is due to spin disorder scattering (increasing with TT), CPA bandstructure renormalization and charged impurity scattering (decreasing with TT). The calculated transport coefficients are discussed in relation to experiment, with a view of assessing the overall trends and deciding whether the model describes the right physics. This does indeed appear to be case, bearing in mind that the hopping limit needs to be treated separately, as it cannot be described within the band CPA.Comment: submitted to Phys. Rev.

    Who are the Customers?

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    Semi-Classical Wavefunction Perspective to High-Harmonic Generation

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    We introduce a semi-classical wavefunction (SCWF) model for strong-field physics and attosecond science. When applied to high harmonic generation (HHG), this formalism allows one to show that the natural time-domain separation of the contribution of ionization, propagation and recollisions to the HHG process leads to a frequency-domain factorization of the harmonic yield into these same contributions, for any choice of atomic or molecular potential. We first derive the factorization from the natural expression of the dipole signal in the temporal domain by using a reference system, as in the quantitative rescattering (QRS) formalism [J. Phys. B. 43, 122001 (2010)]. Alternatively, we show how the trajectory component of the SCWF can be used to express the factorization, which also allows one to attribute individual contributions to the spectrum to the underlying trajectories

    Transportation Alternatives for the Nation

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    Federal and State Funding Legislation

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    Mediators of change in the stigmatization of depression among Caucasian and Asian populations

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    Public stigma negatively impacts public health by discouraging people with depression from seeking help. In North America, Asians reliably report higher levels of stigma and lower levels of help-seeking than do Caucasians. The reasons for this discrepancy and possible methods of reducing this have, however, rarely been explored. In Study 1, undergraduate students (n = 573) completed several questionnaires related to public stigma, values and ideological beliefs, attitudes and beliefs regarding people with depression and perceived norms. At least one week afterward, participants completed the second part of Study 1, where they were presented with contrived articles highlighting a biological cause for depression, a contextual causal for depression, or hope for recovery from depression, or were assigned to a control condition. Asian participants reported higher levels of stigma and increased desired social distance from people with depression compared to Caucasian participants. This difference was mediated by perceived norms, social dominance orientation, conservatism, and the belief that people with depression brings shame to their families. The articles presented were largely ineffective in reducing stigma or desired social distance. In Study 2, undergraduate students (n = 287), were presented with one of four anti-stigma videos with two actresses portraying a student with depression and a professor, respectively. The videos used the concept of social proof to effect change and presented either positive or negative descriptive norms. All videos were effective in reducing preferred social distance towards people with depression relative to the control condition for Asians, but not Caucasians. The effectiveness of the positive descriptive norm video was mediated through perceived norms, empathy, and self-efficacy. The effectiveness of the negative norm video was mediated through perceived norms and empathy only. Differences in preferred social distance between Asian and Caucasian participants were no longer significant. The findings can help guide interventions encouraging social engagement with people with depression among Asian student populations. Manipulating social norms and increasing self-efficacy may be especially effective, while changing attitudes may be less important in an Asian student population

    Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study

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    We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder diffraction experiments and electronic structure calculations. These alloys crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn sites (4c and 4c). The neutron data show that the substituting Fe atoms predominantly occupy the 4c transition metal site and carry a lower magnetic moment than Mn atoms. Four kinds of magnetic structures are encountered as a function of temperature and composition: two simple ferromagnetic structures (with the magnetic moments pointing along the b or c axis) and two canted ferromagnetic arrangements (with the ferromagnetic component pointing along the b or c axis). Electronic structure calculations results agree well with the low-temperature experimental magnetic moments and canting angles throughout the series. Comparisons between collinear and non-collinear computations show that the canted state is stabilized by a band mechanism through the opening of a hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This lowering of symmetry could explain the stabilization of the c-axis canted ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a circumstance that would otherwise require unusually large high-order terms in the spin Hamiltonian.Comment: 11 pages, 13 figure

    Black hole-neutron star mergers: effects of the orientation of the black hole spin

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    The spin of black holes in black hole-neutron star (BHNS) binaries can have a strong influence on the merger dynamics and the postmerger state; a wide variety of spin magnitudes and orientations are expected to occur in nature. In this paper, we report the first simulations in full general relativity of BHNS mergers with misaligned black hole spin. We vary the spin magnitude from a/m=0 to a/m=0.9 for aligned cases, and we vary the misalignment angle from 0 to 80 degrees for a/m=0.5. We restrict our study to 3:1 mass ratio systems and use a simple Gamma-law equation of state. We find that the misalignment angle has a strong effect on the mass of the postmerger accretion disk, but only for angles greater than ~ 40 degrees. Although the disk mass varies significantly with spin magnitude and misalignment angle, we find that all disks have very similar lifetimes ~ 100ms. Their thermal and rotational profiles are also very similar. For a misaligned merger, the disk is tilted with respect to the final black hole's spin axis. This will cause the disk to precess, but on a timescale longer than the accretion time. In all cases, we find promising setups for gamma-ray burst production: the disks are hot, thick, and hyperaccreting, and a baryon-clear region exists above the black hole.Comment: 15 pages, 13 figure
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