15,448 research outputs found
Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence
We present a method for monitoring crystal orientations in chemically polished and unpassivated multicrystalline silicon wafers based on band-to-band photoluminescence imaging. The photoluminescence intensity from such wafers is dominated by surface recombination, which is crystal orientation dependent. We demonstrate that a strong correlation exists between the surface energy of different grain orientations, which are modelled based on first principles, and their corresponding photoluminescence intensity. This method may be useful in monitoring mixes of crystal orientations in multicrystalline or so-called “cast monocrystalline” wafers.H. C. Sio acknowledges scholarship support from
BT Imaging and the Australian Solar Institute, and the
Centre for Advanced Microscopy at ANU for SEM access.
This work has been supported by the Australian Research
Council
The effect of discrete breathers on heat conduction in nonlinear chains
Intensive studies in the past decades have suggested that the heat
conductivity diverges with the system size as in one dimensional momentum conserving nonlinear lattices and the
value of is universal. But in the Fermi-Pasta-Ulam- lattices
with next-nearest-neighbor interactions we find that strongly depends
on , the ratio of the next-nearest-neighbor coupling to the
nearest-neighbor coupling. We relate the -dependent heat conduction to
the interactions between the long-wavelength phonons and the randomly
distributed discrete breathers. Our results provide an evidence to show that
the nonlinear excitations affect the heat transport.Comment: 4 pages, 5 figure
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A novel element upstream of the Vgamma2 gene in the murine T cell receptor gamma locus cooperates with the 3 enhancer to act as a locus control region.
Transgenic expression constructs were employed to identify a cis-acting transcription element in the T cell receptor (TCR)-gamma locus, called HsA, between the Vgamma5 and Vgamma2 genes. In constructs lacking the previously defined enhancer (3E(Cgamma1)), HsA supports transcription in mature but not immature T cells in a largely position-independent fashion. 3E(Cgamma1), without HsA, supports transcription in immature and mature T cells but is subject to severe position effects. Together, the two elements support expression in immature and mature T cells in a copy number-dependent, position-independent fashion. Furthermore, HsA was necessary for consistent rearrangement of transgenic recombination substrates. These data suggest that HsA provides chromatin-opening activity and, together with 3E(Cgamma1), constitutes a T cell-specific locus control region for the TCR-gamma locus
Subunit rearrangement of the cyclin-dependent kinases is associated with cellular transformation
In normal human diploid fibroblasts, cyclins of the A, B, and D classes each associate with cyclin-dependent kinases (CDKs), proliferating cell nuclear antigen (PCNA), and p21, thereby forming multiple independent quaternary complexes. Upon transformation of diploid fibroblasts with the DNA tumor virus SV40, or its transforming tumor antigen (T), the cyclin D/p21/CDK/PCNA complexes are disrupted. In transformed cells, CDK4 totally dissociates from cyclin D, PCNA, and p21 and, instead, associates exclusively with a polypeptide of 16 kD (p16). Quaternary complexes containing cyclins A or B1 and p21/CDK/PCNA also undergo subunit rearrangement in transformed cells. Both PCNA and p21 are no longer associated with CDC2-cyclin B1 binary complexes. Cyclin A complexes no longer contain p21, and a new 19-kD polypeptide (p19) is found in association with cyclin A. The pattern of subunit rearrangement of cyclin-CDK complexes in SV40-transformed cells is also shared in those containing adeno- or papilloma viral oncoproteins. Rearrangement also occurs in p53-deficient cells derived from Li-Fraumeni patients that carry no known DNA tumor virus. These findings suggest a mechanism by which oncogenic proteins alter the cell cycle of transformed cells
The Impacts of Climate Change on Chinese Agriculture - Phase II National Level Study final report
Inverse Magnetoresistance of Molecular Junctions
We present calculations of spin-dependent electron transport through single
organic molecules bridging pairs of iron nanocontacts. We predict the
magnetoresistance of these systems to switch from positive to negative with
increasing applied bias for both conducting and insulating molecules. This
novel inverse magnetoresistance phenomenon is robust, does not depend on the
presence of impurities, and is unique to molecular and atomic nanoscale
magnetic junctions. Its physical origin is identified and its relevance to
experiment and to potential technological applications is discussed.Comment: 5 pages, 3 figures; published version Phys. Rev.
Conductance Correlations Near Integer Quantum Hall Transitions
In a disordered mesoscopic system, the typical spacing between the peaks and
the valleys of the conductance as a function of Fermi energy is called
the conductance energy correlation range . Under the ergodic hypothesis,
the latter is determined by the half-width of the ensemble averaged conductance
correlation function: . In
ordinary diffusive metals, , where is the diffusion constant
and is the linear dimension of the phase-coherent sample. However, near a
quantum phase transition driven by the location of the Fermi energy , the
above picture breaks down. As an example of the latter, we study, for the first
time, the conductance correlations near the integer quantum Hall transitions of
which is a critical coupling constant. We point out that the behavior of
is determined by the interplay between the static and the dynamic
properties of the critical phenomena.Comment: 4 pages, 4 figures, minor corrections, to appear in Phys. Rev. Let
Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films
Superconducting quantum phase transitions tuned by disorder (d), paramagnetic
impurity (MI) and perpendicular magnetic field (B) have been studied in
homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is
characterized by progressive suppression of the critical temperature to zero
and a continuous transition to a weakly insulating normal state with increasing
MI density. In all important aspects, the d-tuned transition closely resembles
the MI-tuned transition and both appear to be fermionic in nature. The B-tuned
transition is qualitatively different and probably bosonic. In the critical
region it exhibits transport behavior that suggests a B-induced mesoscale phase
separation and presence of Cooper pairing in the insulating state.Comment: 17 pages, 4 figure
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