1,283 research outputs found
A general model for collaboration networks
In this paper, we propose a general model for collaboration networks.
Depending on a single free parameter "{\bf preferential exponent}", this model
interpolates between networks with a scale-free and an exponential degree
distribution. The degree distribution in the present networks can be roughly
classified into four patterns, all of which are observed in empirical data. And
this model exhibits small-world effect, which means the corresponding networks
are of very short average distance and highly large clustering coefficient.
More interesting, we find a peak distribution of act-size from empirical data
which has not been emphasized before of some collaboration networks. Our model
can produce the peak act-size distribution naturally that agrees with the
empirical data well.Comment: 10 pages, 10 figure
Ground-State Spaces of Frustration-Free Hamiltonians
We study the ground-state space properties for frustration-free Hamiltonians.
We introduce a concept of `reduced spaces' to characterize local structures of
ground-state spaces. For a many-body system, we characterize mathematical
structures for the set of all the -particle reduced spaces, which
with a binary operation called join forms a semilattice that can be interpreted
as an abstract convex structure. The smallest nonzero elements in ,
called atoms, are analogs of extreme points. We study the properties of atoms
in and discuss its relationship with ground states of -local
frustration-free Hamiltonians. For spin-1/2 systems, we show that all the atoms
in are unique ground states of some 2-local frustration-free
Hamiltonians. Moreover, we show that the elements in may not be the
join of atoms, indicating a richer structure for beyond the convex
structure. Our study of deepens the understanding of ground-state
space properties for frustration-free Hamiltonians, from a new angle of reduced
spaces.Comment: 23 pages, no figur
Quantum Capacity Approaching Codes for the Detected-Jump Channel
The quantum channel capacity gives the ultimate limit for the rate at which
quantum data can be reliably transmitted through a noisy quantum channel.
Degradable quantum channels are among the few channels whose quantum capacities
are known. Given the quantum capacity of a degradable channel, it remains
challenging to find a practical coding scheme which approaches capacity. Here
we discuss code designs for the detected-jump channel, a degradable channel
with practical relevance describing the physics of spontaneous decay of atoms
with detected photon emission. We show that this channel can be used to
simulate a binary classical channel with both erasures and bit-flips. The
capacity of the simulated classical channel gives a lower bound on the quantum
capacity of the detected-jump channel. When the jump probability is small, it
almost equals the quantum capacity. Hence using a classical capacity
approaching code for the simulated classical channel yields a quantum code
which approaches the quantum capacity of the detected-jump channel
Nonequilibrium Atom-Dielectric Forces Mediated by a Quantum Field
In this paper we give a first principles microphysics derivation of the
nonequilibrium forces between an atom, treated as a three dimensional harmonic
oscillator, and a bulk dielectric medium modeled as a continuous lattice of
oscillators coupled to a reservoir. We assume no direct interaction between the
atom and the medium but there exist mutual influences transmitted via a common
electromagnetic field. By employing concepts and techniques of open quantum
systems we introduce coarse-graining to the physical variables - the medium,
the quantum field and the atom's internal degrees of freedom, in that order -
to extract their averaged effects from the lowest tier progressively to the top
tier. The first tier of coarse-graining provides the averaged effect of the
medium upon the field, quantified by a complex permittivity (in the frequency
domain) describing the response of the dielectric to the field in addition to
its back action on the field through a stochastic forcing term. The last tier
of coarse- graining over the atom's internal degrees of freedom results in an
equation of motion for the atom's center of mass from which we can derive the
force on the atom. Our nonequilibrium formulation provides a fully dynamical
description of the atom's motion including back action effects from all other
relevant variables concerned. In the long-time limit we recover the known
results for the atom-dielectric force when the combined system is in
equilibrium or in a nonequilibrium stationary state.Comment: 24 pages, 2 figure
Sources and production of organic aerosol in Mexico City: insights from the combination of a chemical transport model (PMCAMx-2008) and measurements
Urban areas are large sources of organic aerosols and their precursors. Nevertheless, the contributions of primary (POA) and secondary organic aerosol (SOA) to the observed particulate matter levels have been difficult to quantify. In this study the three-dimensional chemical transport model PMCAMx-2008 is used to investigate the temporal and geographic variability of organic aerosol in the Mexico City Metropolitan Area (MCMA) during the MILAGRO campaign that took place in the spring of 2006. The organic module of PMCAMx-2008 includes the recently developed volatility basis-set framework in which both primary and secondary organic components are assumed to be semi-volatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The MCMA emission inventory is modified and the POA emissions are distributed by volatility based on dilution experiments. The model predictions are compared with observations from four different types of sites, an urban (T0), a suburban (T1), a rural (T2), and an elevated site in Pico de Tres Padres (PTP). The performance of the model in reproducing organic mass concentrations in these sites is encouraging. The average predicted PM[subscript 1] organic aerosol (OA) concentration in T0, T1, and T2 is 18 μg m[superscript −3], 11.7 μg m[superscript −3], and 10.5 μg m[superscript −3] respectively, while the corresponding measured values are 17.2 μg m[superscript −3], 11 μg m[superscript −3], and 9 μg m[superscript −3]. The average predicted locally-emitted primary OA concentrations, 4.4 μg m[superscript −3] at T0, 1.2 μg m[superscript −3] at T1 and 1.7 μg m[superscript −3] at PTP, are in reasonably good agreement with the corresponding PMF analysis estimates based on the Aerosol Mass Spectrometer (AMS) observations of 4.5, 1.3, and 2.9 μg m[superscript −3] respectively. The model reproduces reasonably well the average oxygenated OA (OOA) levels in T0 (7.5 μg m[superscript −3] predicted versus 7.5 μg m[superscript −3] measured), in T1 (6.3 μg m[superscript −3] predicted versus 4.6 μg m[superscript −3] measured) and in PTP (6.6 μg m[superscript −3] predicted versus 5.9 μg m[superscript −3] measured). The rest of the OA mass (6.1 μg m[superscript −3] and 4.2 μg m[superscript −3] in T0 and T1 respectively) is assumed to originate from biomass burning activities and is introduced to the model as part of the boundary conditions. Inside Mexico City (at T0), the locally-produced OA is predicted to be on average 60 % locally-emitted primary (POA), 6 % semi-volatile (S-SOA) and intermediate volatile (I-SOA) organic aerosol, and 34 % traditional SOA from the oxidation of VOCs (V-SOA). The average contributions of the OA components to the locally-produced OA for the entire modelling domain are predicted to be 32 % POA, 10 % S-SOA and I-SOA, and 58 % V-SOA. The long range transport from biomass burning activities and other sources in Mexico is predicted to contribute on average almost as much as the local sources during the MILAGRO period.European UnionSeventh Framework Programme (European Commission) (Grant agreement no.: 212520)National Science Foundation (U.S.) (ATM 0732598)Molina Center for Energy and the EnvironmentNational Science Foundation (U.S.) (ATM 0528227)National Science Foundation (U.S.) (ATM 0810931
Monolithic growth of InAs quantum dots lasers on (001) silicon emitting at 1.55 μm
Broad-area 1.55 μm InAs quantum dots (QDs) lasers were fabricated based on monolithic growth of InAs/InAlGaAs/InP active structures on nano-patterned (001) silicon substrates. Device optoelectronic properties and materials' optical gain and absorption features were studied to provide experimental support for further optimizations in laser design
Daya Tahan Spermatozoa Dalam Semen Cair Babi Landrace Pada Metode Penyimpanan Berbeda
Tujuan dilaksanakan penelitian ini untuk melihat pengaruh metode penyimpanan preservasi yang berbeda terhadap viabilitas spermatozoa semen babi landrace dalam pengencer alami air buah lontar (AL) dengan penambahan kuning telur ayam kampung (KT). Semen diambil dari 5 ekor pejantan landrace yang telah dewasa kelamin. Setelah itu dilakukan pemeriksaan makros-mikros dari semen segar, semen dengan kriteria motilitas , konsentrasi dan abnormalitas spermatozoa berturt-turut: >70%, >200 juta spermatozoa/ml, <20% yang layak untuk dijadikan semen cair. Perlakuan dalam penelitian:, P1(AL 95%+5% KT), P2(AL 85%+15% KT), P3(AL 75%+25% KT) yang simpan pada metode water jacket (WJ) dan P4(AL 95%+5% KT), P5(AL 85%+15% KT), P6(AL 75%+25% KT) yang disimpan dengan metode non water jacket (NWJ), semen dikemas dalam mikrotube 1 ml dan disimpan pada suhu preservasi. Pada penelitian ini menunjukkan bahwa viabilitas spermatozooa dalam pengencer alami air buah lontar yang ditambahkan dengan kuning telur ayam kampung memperlihatkan hasil yang baik pada kombinasi AL 85% dan KT25% pada penyimpanan water jacket. Semen cair pada pengencer kombinasi tersebut diatas mampu bertahan hingga 28 jam penyimpanan
DNAM-1-chimeric receptor-engineered NK cells, combined with Nutlin-3a, more effectively fight neuroblastoma cells in vitro: a proof-of-concept study.
Natural humoral immune response to ribosomal P0 protein in colorectal cancer patients
Tumor associated antigens are useful in colorectal cancer (CRC) management. The ribosomal P proteins (P0, P1, P2) play an important role in protein synthesis and tumor formation. The immunogenicity of the ribosomal P0 protein in head and neck, in breast and prostate cancer patients and the overexpression of the carboxyl-terminal P0 epitope (C-22 P0) in some tumors were reported
Gene-specific inhibition of breast carcinoma in BALB-neuT mice by active immunization with rat Neu or human ErbB receptors
Employing the transgenic BALB-neuT mouse tumor model, we explored the in vivo biologic relevance of immunocompetent epitopes shared among the four ErbB receptors. The outcome of neu-mediated tumorigenesis was compared following vaccination with isogeneic normal rat ErbB2/Neu (LTR-Neu) or xenogeneic human ErbB receptors (LTR-EGFR, LTR-ErbB2, LTR-ErbB3 and LTR-ErbB4), each recombinantly expressed in an NIH3T3 murine cell background. Vaccination using rat LTR-Neu at the stage of atypical hyperplasia potently inhibited neu-mediated mammary tumorigenesis. Moreover, all human ErbB receptors specifically interfered with tumor development in BALB-neuT mice. Relative increase in tumor-free survival and reduction in tumor incidence corresponded to structural similarity shared with the etiologic neu oncogene, as rat orthologue LTR-Neu proved most effective followed by the human homologue LTR-ErbB2 and the other three human ErbB receptors. Vaccination resulted in high titer specific serum antibodies, whose tumor-inhibitory effect correlated with cross-reactivity to purified rat Neu extracellular domain in vitro. Furthermore, a T cell response specific for peptide epitopes of rat Neu was elicited in spleen cells of mice immunized with LTR-Neu and was remotely detectable for discrete peptides upon vaccination with LTR-ErbB2 and LTR-EGFR. The most pronounced tumor inhibition by LTR-Neu vaccination was associated with leukocyte infiltrate and tumor necrosis in vivo, while immune sera specifically induced cytotoxicity and apoptosis of BALB-neuT tumor cells in vitro. Our findings indicated that targeted inhibition of neu oncogene-mediated mammary carcinogenesis is conditional upon the immunization schedule and discrete immunogenic epitopes shared to a variable extent by different ErbB receptors
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