cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Growth of accretion driven scalar hair around Kerr black holes
Creators: name: Bamber, Jamie
name: Clough, Katy
name: Ferreira, Pedro G.
name: Hui, Lam
name: Lagos, Macarena
Publisher: name: arXiv
Year: 2020
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: Scalar fields around compact objects are of interest for scalar-tensor theories of gravity and dark matter models consisting of a massive scalar, e.g. axions. We study the behaviour of a scalar field around a Kerr black hole with non trivial asymptotic boundary conditions - both non zero density and non zero angular momentum. Starting from an initial radially homogeneous configuration, a scalar cloud is accreted, which asymptotes to known stationary configurations over time. We study the cloud growth for different parameters including black hole spin, scalar field mass, and the scalar field density and angular momentum far from the black hole. We characterise the transient growth of the mass and angular momentum in the cloud, and the spatial profile of the scalar around the black hole, and relate the results of fully non-linear simulations to an analytic perturbative expansion. We also highlight the potential for these accreted clouds to create monochromatic gravitational wave signals - similar to the signals from superradiant clouds, although significantly weaker in amplitude.
description: 21 pages, 24 figures
กลวิธีทางภาษาที่ใช้ในพระราชดำรัสในพระบาทสมเด็จพระจุลจอมเกล้าเจ้าอยู่หัว (พ.ศ. ๒๔๑๗-๒๔๕๓): การศึกษาจากมุมมองวัจนปฏิบัติศาสตร์
Creators: name: สิทธิธรรม อ่องวุฒิวัฒน์
Publisher: name: คณะศิลปศาสตร์ มหาวิทยาลัยธรรมศาสตร์
Year: 2016
Subjects: -

description: วรรณวิทัศน์, 16, พฤศจิกายน, 101-134
Cost-Effectiveness of On-Farm Conservation Practices to Protect Playa Lake Hydroperiod in the Texas High Plains
Creators: name: Willis, David B.
name: Willis, David B.
Publisher: name: Unknown
Year: 2008
Subjects: Land Economics/Use
Resource /Energy Economics and Policy

description: Estimating the agricultural cost of using buffer strips and/or furrow dikes as on-farm control measures to reduce sedimentation run-off from agricultural cropland into the playa wetlands of the Texas High Plains (THP) for the purpose of increasing/preserving playa hydroperiod and protect the unique playa lake wetland systems in the THP.
Characterization of strong light-matter coupling in semiconductor quantum-dot microcavities via photon-statistics spectroscopy
Creators: name: Schneebeli, L.
name: Kira, M.
name: Koch, S. W.
Publisher: name: arXiv
Year: 2008
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: It is shown that spectrally resolved photon-statistics measurements of the resonance fluorescence from realistic semiconductor quantum-dot systems allow for high contrast identification of the two-photon strong-coupling states. Using a microscopic theory, the second-rung resonance is analyzed and optimum excitation conditions are determined. The computed photon-statistics spectrum displays gigantic, experimentally robust resonances at the energetic positions of the second-rung emission.
description: 4 pages, 2 figures
ความเชื่อที่สะท้อนจากชื่อเรือยาวภาคตะวันออกเฉียงเหนือ
Creators: name: พรเพ็ญ เหล็กดีเศษ
Publisher: name: คณะศิลปศาสตร์ มหาวิทยาลัยธรรมศาสตร์
Year: 2016
Subjects: -

description: วรรณวิทัศน์, 16, พฤศจิกายน, 135-160
Correlated Insulating Phases in the Twisted Bilayer Graphene
Creators: name: Da Liao, Yuan
name: Xu, Xiao Yan
name: Meng, Zi Yang
name: Kang, Jian
Publisher: name: arXiv
Year: 2020
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: We review analytical and numerical studies of correlated insulating states in twisted bilayer graphene, focusing on real-space lattice models constructions and their unbiased quantum many-body solutions. We show that by constructing localized Wannier states for the narrow bands, the projected Coulomb interactions can be approximated by interactions of cluster charges with assisted nearest neighbor hopping terms. With the interaction part only, the Hamiltonian is $SU(4)$ symmetric considering both spin and valley degrees of freedom. In the strong coupling limit where the kinetic terms are neglected, the ground states are found to be in the $SU(4)$ manifold with degeneracy. The kinetic terms, treated as perturbation, break this large $SU(4)$ symmetry and propel the appearance of intervalley coherent state, quantum topological insulators and other symmetry-breaking insulating states. We first present the theoretical analysis of moiré lattice model construction and then show how to solve the model with large-scale quantum Monte Carlo simulations in an unbiased manner. We further provide potential directions such that from the real-space model construction and its quantum many-body solutions how the perplexing yet exciting experimental discoveries in the correlation physics of twisted bilayer graphene can be gradually understood. This review will be helpful for the readers to grasp the fast growing field of the model study of twisted bilayer graphene.
description: 15 pages, 12 figures, invited review article
Millihertz Quasi-Periodic Oscillations from Marginally Stable Nuclear Burning on an Accreting Neutron Star
Creators: name: Heger, Alexander
name: Cumming, Andrew
name: Woosley, Stanford E.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We investigate marginally stable nuclear burning on the surface of accreting neutron stars as an explanation for the mHz quasi-periodic oscillations (QPOs) observed from three low mass X-ray binaries. At the boundary between unstable and stable burning, the temperature dependence of the nuclear heating rate and cooling rate almost cancel. The result is an oscillatory mode of burning, with an oscillation period close to the geometric mean of the thermal and accretion timescales for the burning layer. We describe a simple one-zone model which illustrates this basic physics, and then present detailed multizone hydrodynamical calculations of nuclear burning close to the stability boundary using the KEPLER code. Our models naturally explain the characteristic 2 minute period of the mHz QPOs, and why they are seen only in a very narrow range of X-ray luminosities. The oscillation period is sensitive to the accreted hydrogen fraction and the surface gravity, suggesting a new way to probe these parameters. A major puzzle is that the accretion rate at which the oscillations appear in the theoretical models is an order of magnitude larger than the rate implied by the X-ray luminosity when the mHz QPOs are seen. We discuss the implications for our general understanding of nuclear burning on accreting neutron stars. One possibility is that the accreted material covers only part of the neutron star surface at luminosities Lx > ~1E37 erg/s.
description: 10 pages, 9 figures, submitted to ApJ
Towards Reduced Pesticide Use for Cereal Crops in Asia
Creators: name: Pingali, Prabhu L.
name: Gerpacio, Roberta V.
name: Pingali, Prabhu L.
name: Gerpacio, Roberta V.
Publisher: name: Unknown
Year: 1997
Subjects: Crop Production/Industries

description: Several opportunities are available for dramatically reducing the use of agrochemicals in Asian cereal crop production. The first section of this paper summarizes past trends and future prospects for pesticide use in Asia for the three major cereal crops: rice, wheat, and maize. The second section identifies factors that have contributed to rising farm-level demand for pesticides and factors that could lead to a reduction in their demand. The third section highlights the advances that have been made in generating and disseminating cereal crops with resistance to insects and diseases. It focuses on conventional breeding strategies for host-plant resistance as well as the current and potential contributions of biotechnology. Pesticide productivity, yield variability, and their relation to host-plant resistance are reviewed, along with evidence from trials and farmers' fields. The paper concludes with a discussion of the integrated management approaches that will be necessary for maximizing and sustaining the productivity gains offered by resistant varieties.
ภาพสะท้อนภาษาไทยถิ่นในสื่อมวลชน
Creators: name: อรวี บุญนาค
Publisher: name: คณะศิลปศาสตร์ มหาวิทยาลัยธรรมศาสตร์
Year: 2016
Subjects: -

description: วรรณวิทัศน์, 16, พฤศจิกายน, 161-191
Spectral form factor in the double-scaled SYK model
Creators: name: Khramtsov, Mikhail
name: Lanina, Elena
Publisher: name: arXiv
Year: 2020
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: In this note we study the spectral form factor in the SYK model in large $q$ limit at infinite temperature. We construct analytic solutions for the saddle point equations that describe the slope and the ramp regions of the spectral form factor time dependence. These saddle points are obtained by taking different approaches to the large $q$ limit: the slope region is described by a replica-diagonal solution and the ramp region is described by a replica-nondiagonal solution. We find that the onset of the ramp behavior happens at the Thouless time of order $q \log q$. We also evaluate the one-loop corrections to the slope and ramp solutions for late times, and study the transition from the slope to the ramp. We show this transition is accompanied by the breakdown of the perturbative $1/q$ expansion, and that the Thouless time is defined by the consistency of extrapolation of this expansion to late times.
description: 34+9 pages, 14 figures. v2: added reference, published version
Finite hadronization time and unitarity in quark recombination model
Creators: name: Yang, C. B.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Nuclear Theory (nucl-th)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: Nuclear Experiment (nucl-ex)
subject: FOS: Physical sciences

description: The effect of finite hadronization time is considered in the recombination model, and it is shown that the hadron multiplicity turns out to be proportional to the initial quark density and unitarity is conserved in the model. The baryon to meson ratio increases rapidly with the initial quark density due to competition among different channels.
description: 4 pages in RevTeX, 3 eps figures, to appear in J. Phys.G as a letter
The Contribution of Genetic Resources and Diversity to Wheat Productivity: A Case from the Punjab of Pakistan
Creators: name: Hartell, Jason G.
name: Smale, Melinda
name: Heisey, Paul W.
name: Senauer, Benjamin
name: Hartell, Jason G.
name: Smale, Melinda
name: Heisey, Paul W.
name: Senauer, Benjamin
Publisher: name: Unknown
Year: 1997
Subjects: Crop Production/Industries

description: This study makes use of data on wheat production in the Punjab of Pakistan from 1979 to 1985 to 1) examine patterns of varietal diversity in farmers' fields both at the regional and district levels and 2) identify how and in what ways genetic resources have contributed to wheat productivity and yield stability-important considerations to farmers and national authorities where wheat is a staple food crop. Five indicators are used to describe the system of wheat genetic resource use and diversity in farmers' fields. The contribution of farmers' previous selections is expressed as the number of different landraces appearing in the pedigree of a cultivar . The contribution of scientific breeding efforts is expressed as the number of parental combination appearing in a cultivar's pedigree. The diversity of wheat varieties in a geographical area, as related to productivity, is captured by measures of area concentration (diversity in space) and age of varieties (diversity in time). Finally, the relative dissimilarity of cultivars grown in a geographical area is measured using a distance indicator constructed from genealogical information. Disaggregated analysis at the district level demonstrates how diversity patterns are influenced by the production environment and by possible differences in the availability of suitable varieties. The study finds no indication that modern plant breeding technologies have reduced diversity among the wheats grown in the districts of the Punjab of Pakistan during the study period, although brief. Analysis of the genealogical background of the varieties grown by farmers reveals patterns of greater use of genetic resources and dissimilarity of parentage. For some factors related to genetic resource use and diversity, there are large differences between production environments (specifically, irrigated and rainfed areas) and individual districts, which suggest that efforts to increase genetic diversity in farmers' fields will require policy instruments tailored to the individual circumstances of each production environment. Econometric results suggest that greater genealogical dissimilarity and higher rates of varietal replacement are likely to have positive payoffs relative to aggregate yield stability, while in areas where production constraints inhibit farmers' ability to exploit the yield potential of their varieties, better production management is likely to have greater yield enhancing effects than the varietal attributes related to diversity.
Integration of navigation and action selection functionalities in a computational model of cortico-basal ganglia-thalamo-cortical loops
Creators: name: Girard, Benoît
name: Filliat, David
name: Meyer, Jean-Arcady
name: Berthoz, Alain
name: Guillot, Agnès
Publisher: name: arXiv
Year: 2006
Subjects: subject: Artificial Intelligence (cs.AI)
subject: Robotics (cs.RO)
subject: FOS: Computer and information sciences

description: This article describes a biomimetic control architecture affording an animat both action selection and navigation functionalities. It satisfies the survival constraint of an artificial metabolism and supports several complementary navigation strategies. It builds upon an action selection model based on the basal ganglia of the vertebrate brain, using two interconnected cortico-basal ganglia-thalamo-cortical loops: a ventral one concerned with appetitive actions and a dorsal one dedicated to consummatory actions. The performances of the resulting model are evaluated in simulation. The experiments assess the prolonged survival permitted by the use of high level navigation strategies and the complementarity of navigation strategies in dynamic environments. The correctness of the behavioral choices in situations of antagonistic or synergetic internal states are also tested. Finally, the modelling choices are discussed with regard to their biomimetic plausibility, while the experimental results are estimated in terms of animat adaptivity.
Baryonic Tully-Fisher Relation for Extremely Low Mass Galaxies
Creators: name: Begum, Ayesha
name: Chengalur, Jayaram N.
name: Karachentsev, I. D.
name: Sharina, M. E.
Publisher: name: arXiv
Year: 2008
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We study Tully-Fisher relations for a sample that combines extremely faint (M_B > -14.0) galaxies along with bright (i.e. L_*) galaxies. Accurate (~ 10%) distances, I band photometry, and B-V colors are known for the majority of the galaxies in our sample. The faint galaxies are drawn from the Faint Irregular Galaxy GMRT survey (FIGGS), and we have HI rotation velocities derived from aperture synthesis observations for all of them. For the faint galaxies, we find that even though the median HI and stellar masses are comparable, the HI mass correlates significantly better with the circular velocity indicators than the stellar mass. We also find that W$_{20}$ correlates better with mass than the rotation velocity, although the difference is not statistically significant. The faint galaxies lie systematically below the I band TF relation defined by bright galaxies, and also show significantly more intrinsic scatter. This implies that the integrated star formation in these galaxies has been both less efficient and also less regulated than in large galaxies. We find that while the faint end deviation is greatly reduced in Baryonic Tully-Fisher (BTF) relations, the existence of a break at the faint end of the BTF is subject to systematics such as the assumed stellar mass to light ratio. If we assume that there is an intrinsic BTF and try to determine the baryonic mass by searching for prescriptions that lead to the tightest BTF, we find that scaling the HI mass leads to a much more significant tightening than scaling the stellar mass to light ratio. The most significant tightening that we find however, is if we scale the entire baryonic mass of the faint (but not the bright) galaxies. Such a scenario would be consistent with models where dwarf (but not large) galaxies have a large fraction of dark or ``missing'' baryons (Slightly abridged)
description: 7 pages, 7 figures. Accepted for publication in MNRAS
Neutrinos: the Key to UHE Cosmic Rays
Creators: name: Seckel, David
name: Stanev, Todor
Publisher: name: arXiv
Year: 2005
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely determine both the injection spectrum and the evolution model for UHECR sources - primarily because interactions during propagation obscure the early Universe from direct observation. Detection of neutrinos produced in those same interactions, coupled with UHECR results, would provide a full description of UHECR source properties.
description: three pages, three figures. corrected typos
Phase Diagram of Infinite Layer Praseodymium Nickelate Pr$_{1-x}$Sr$_{x}$NiO$_2$ Thin Films
Creators: name: Osada, Motoki
name: Wang, Bai Yang
name: Lee, Kyuho
name: Li, Danfeng
name: Hwang, Harold Y.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: We report the phase diagram of infinite layer Pr$_{1-x}$Sr$_{x}$NiO$_2$ thin films synthesized via topotactic reduction from the perovskite precursor phase using CaH$_2$. Based on the electrical transport properties, we find a doping-dependent superconducting dome extending between $x$ = 0.12 and 0.28, with a maximum superconducting transition temperature $T_{\rm{c}}$ of 14 K at $x$ = 0.18, bounded by weakly insulating behavior on both sides. In contrast to the narrower dome observed in Nd$_{1-x}$Sr$_{x}$NiO$_2$, a local $T_{\rm{c}}$ suppression near $x$ = 0.2 was not observed for the Pr$_{1-x}$Sr$_{x}$NiO$_2$ system. Normal state Hall effect measurements indicate mixed carrier contributions of both electrons and holes, and show a sign change in the Hall coefficient as functions of temperature and $x$, quite similar to that in Nd$_{1-x}$Sr$_{x}$NiO$_2$. Also similar is the observation of a minimum in the normal state resistivity associated with the superconducting compositions. These findings indicate an infinite layer nickelate phase diagram that is relatively insensitive to the rare-earth element, but suggest that disorder arising from the variations of the ionic radii on the rare-earth site affects the superconducting dome.
description: 17 pages, 3 figures
Institutional Change and Discontinuities in Farmers' Use of Hybrid Maize Seed and Fertilizer in Malawi: Findings from the 1996-97 CIMMYT/ MoALD Survey
Creators: name: Smale, Melinda
name: Phiri, Alexander
name: Smale, Melinda
name: Phiri, Alexander
Publisher: name: Unknown
Year: 1998
Subjects: Crop Production/Industries

description: This study records the use of hybrid maize seed and fertilizer by small-scale farmers in Malawi, as well as their opinions about these inputs, from 1989-90 through 1996-97. Its main purpose is to determine whether the principal constraint to smallholders' use of maize hybrids is the acceptability of the hybrid maize germplasm or the institutional reforms and policies affecting its use. The study also provides information about a practice that has implications for the impact of seed technologies and seed industries - the recycling of nonconventional hybrids (i.e., saving seed of an F1 hybrid to plant in subsequent seasons). Findings of the most recent farmer survey in 1996-97 demonstrate that the grain quality or yield characteristics of maize hybrids no longer constrain smallholders' use of F1 hybrid seed. Farmers stated almost unanimously that they wanted to grow F1 hybrid seed, but most could not purchase as much seed as they wished. A large number of farmers recycle hybrid seed, which is not surprising, given the early stages of diffusion of hybrid maize in Malawi, the start-stop nature of policies affecting input use, and free seed distributed by the government and NGOs. It may be worthwhile for researchers to investigate prospects for producing hybrids whose characteristics resist deterioration from recycling. Aside from this plant breeding issue, pressing concerns of national maize production, food security, and the welfare of smallholders remain to be addressed. Farmers with the resources to use credit, purchase inputs, grow cash crops, or produce maize surpluses represent a smaller and smaller percentage of farmers. It is doubtful whether complete reliance on private initiatives can transform the smallholder maize sector in a country that relies on agriculture as much as Malawi, but where infrastructure is inadequate, nonfarm employment opportunities are few, and incentives are insufficient to mobilize trade and generate cash in rural areas.
An Economic Analysis of the Abonera Maize Production System in the Atlantic Coast of Honduras
Creators: name: Sain, Gustavo
name: Buckles, Daniel
name: Sain, Gustavo
name: Buckles, Daniel
Publisher: name: Unknown
Year: 1998
Subjects: Crop Production/Industries

description: This paper compares the economics of the abonera maize production system, in which maize is grown in rotation with a green manure crop (velvetbean, Mucuna deeringiana), with traditional bush-fallow cultivation of maize in the Atlantic Coast area of Honduras. A probabilistic cost-benefit analysis of introducing velvetbean into the existing maize cropping pattern is carried out for the field, farm, and regional level. The probabilistic approach allows for a more comprehensive assessment of economic profitability, one which recognizes that farmers are interested in reducing production risk as well as obtaining increases in average net benefits. The analysis reveals that the abonera system provides significant returns to land and family labor over the six-year life cycle. The abonera is not only more profitable than the bush-fallow system but reduces the variability in economic returns, making second-season maize a less risky production alternative. Although the labor requirement per unit of land is smaller in the abonera system than that in the bush-fallow system, the larger area allocated to maize implies a net increase in labor requirements at the farm level. At the regional level, widespread adoption of the abonera system appears to have increased the importance of the second season in total maize production. Although a causal link to adoption of the abonera system cannot be established conclusively from the data, adoption of the system remains a likely explanation for the changes observed in aggregate maize production in the Atlantic Coast region. Land rental prices for sowing second-season maize also reflect the widespread impact of the abonera system.
Simultaneous NICER and NuSTAR Observations of the Ultra-compact X-ray Binary 4U 1543-624
Creators: name: Ludlam, R. M.
name: Jaodand, A. D.
name: García, J. A.
name: Degenaar, N.
name: Tomsick, J. A.
name: Cackett, E. M.
name: Fabian, A. C.
name: Gandhi, P.
name: Buisson, D. J. K.
name: Shaw, A. W.
name: Chakrabarty, D.
Publisher: name: arXiv
Year: 2020
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: We present the first joint NuSTAR and NICER observations of the ultra-compact X-ray binary (UCXB) 4U 1543$-$624 obtained in 2020 April. The source was at a luminosity of $L_{0.5-50\ \mathrm{keV}} = 4.9 (D/7\ \mathrm{kpc})^{2}\times10^{36}$ ergs s$^{-1}$ and showed evidence of reflected emission in the form of an O VIII line, Fe K line, and Compton hump within the spectrum. We used a full reflection model, known as xillverCO, that is tailored for the atypical abundances found in UCXBs, to account for the reflected emission. We tested the emission radii of the O and Fe line components and conclude that they originate from a common disk radius in the innermost region of the accretion disk ($R_{\rm in} \leq1.07\ R_{\mathrm{ISCO}}$). Assuming that the compact accretor is a neutron star (NS) and the position of the inner disk is the Alfvén radius, we placed an upper limit on the magnetic field strength to be $B\leq0.7(D/7\ \mathrm {kpc})\times10^{8}$ G at the poles. Given the lack of pulsations detected and position of $R_{\rm in}$, it was likely that a boundary layer region had formed between the NS surface and inner edge of the accretion disk with an extent of 1.2 km. This implies a maximum radius of the neutron star accretor of $R_{\mathrm{NS}}\leq 12.1$ km when assuming a canonical NS mass of 1.4 $M_{\odot}$.
description: Accepted for publication in ApJ, 10 pages, 6 figures, 1 table
Farmers' Taxonomies as a Participatory Diagnostic Tool: Soil Fertility Management in Chihota, Zimbabwe
Creators: name: Bellon, Mauricio R.
name: Gambara, Peter
name: Gatsi, Tendai
name: MacHemedze, Timothy E.
name: Maminimini, Obert
name: Waddington, Stephen R.
name: Bellon, Mauricio R.
name: Gambara, Peter
name: Gatsi, Tendai
name: MacHemedze, Timothy E.
name: Maminimini, Obert
name: Waddington, Stephen R.
Publisher: name: Unknown
Year: 1999
Subjects: subject: Farm Management
subject: Land Economics/Use
subject: participatory methods
subject: soil fertility
subject: local taxonomies
subject: smallholders
subject: Zimbabwe

description: Soil infertility is a major constraint to food production in the communal areas of Zimbabwe. Smallholders in the region recognize the problems of low soil fertility and have devised ways of coping with them. This study describes the use of farmers' taxonomies of themselves and their soils to identify and understand the options they have, and the constraints they face in managing poor soil fertility in Chihota, a sub-humid communal area of north central Zimbabwe. It is part of an effort by a group of agricultural researchers and extensionists working on improved soil fertility technologies, to better integrate their work with farmers in order to expose the latter to promising technologies, get feedback on the technologies merits and feasibility, and help farmers experiment with them. The results show that these farmers have relatively sophisticated taxonomies, which provide a good picture of the resources, constraints, and concerns they have about soil infertility and ways to manage it. The taxonomies are an important framework for integration of technical interventions with farmers' requirements, systems, and circumstances.
Accretion and nuclear activity of quiescent supermassive black holes. I: X-ray study
Creators: name: Soria, Roberto
name: Fabbiano, Giuseppina
name: Graham, Alister W.
name: Baldi, Alessandro
name: Elvis, Martin
name: Jerjen, Helmut
name: Pellegrini, Silvia
name: Siemiginowska, Aneta
Publisher: name: arXiv
Year: 2005
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities ~ 10^{38} - 10^{39} erg/s (L_X/L_Edd ~ 10^{-8} - 10^{-7}), and colors or spectra consistent with accreting supermassive black holes (SMBHs)--except for the nucleus of NGC 4486B, which is softer than typical AGN spectra. In a few cases, the X-ray morphology of the nuclear sources shows hints of marginally extended structures, in addition to the surrounding diffuse thermal emission from hot gas, which is detectable on scales >~ 1 kpc. In one case (NGC 5845), a dusty disk may partially obstruct our direct view of the SMBH. We have estimated the temperature and density of the hot interstellar medium, which is one major source of fuel for the accreting SMBH; typical central densities are n_e ~ (0.02 +/- 0.01) cm^{-3}. Assuming that the hot gas is captured by the SMBH at the Bondi rate, we show that the observed X-ray luminosities are too faint to be consistent with standard disk accretion, but brighter than predicted by radiatively-inefficient solutions (eg, ADAF). In total, there are ~ 20 galaxies for which SMBH mass, hot gas density, and nuclear X-ray luminosity are simultaneously known. In some cases, the nuclear sources are brighter than predicted by the ADAF model; in other cases, they are consistent or fainter. We discuss the apparent lack of correlations between Bondi rate and X-ray luminosity, and suggest that, in order to understand the observed distribution, we need to know two additional parameters: the amount of gas supplied by the stellar population inside the accretion radius, and the fraction (possibly << 1) of the total gas available that is accreted by the SMBH. We shall discuss these issues in our Paper II.
description: 18 pages, accepted by ApJ. This is Paper I; Paper II will be on astro-ph next Monday
Analisis del sistema panameno de investigacion agropecuaria
Creators: name: Ekboir, Javier M.
name: De Herrera, Adys Pereira
name: Becerra, Franklin
name: Ekboir, Javier M.
name: De Herrera, Adys Pereira
name: Becerra, Franklin
Publisher: name: Unknown
Year: 2003
Subjects: subject: Research and Development/Tech Change/Emerging Technologies
subject: Panama

description: Panamá tiene una economía dual con unas pocas actividades altamente competitivas y otras que se desarrollaron gracias a políticas de sustitución de importaciones. Estas políticas influyeron sobre el sistema público de investigación. Durante 15 años, los objetivos más importantes de este sistema fueron el apoyo a productores que vendían en el mercado interno y el fomento de las actividades tradicionales de exportación. La competitividad y la comercialización no eran relevantes. Así, las instituciones de investigación desarrollaron programas para los productos tradicionales de los pequeños y medianos productores (granos básicos y ganadería). La estabilidad de las políticas proteccionistas y el deficiente control de la calidad de la investigación permitieron el mantenimiento de programas de trabajo poco relevantes. Al mismo tiempo, las instituciones de investigación y transferencia se organizaron en base a la concepción lineal de la ciencia, que desincentivaba interacciones fuera de las instituciones. Estas políticas se agotaron en la década del 80 y forzaron la implementación de programas de ajuste estructural. En el nuevo entorno las exportaciones se diversificaron gracias a una activa participación del sector privado. La mayor parte de las tecnologías para los productos no tradicionales fue importada. Las instituciones públicas de investigación tuvieron una participación limitada en el desarrollo de tecnologías para estos productos, limitándose a investigaciones relativamente sencillas. Las transformaciones de la economía indujeron la aparición de nuevos agentes innovadores, nuevas fuentes de financiamiento de la investigación y nuevas demandas. En general, las instituciones públicas no han podido adaptarse al entorno más dinámico por la falta de experiencia en la interacción con otros agentes (privados o públicos), por dificultades para adaptarse a cambios externos y porque las modificaciones en los incentivos ofrecidos a investigadores y administradores se han limitado a aspectos de financiamiento, sin considerar el resto de los estímulos, especialmente la calidad de las investigaciones y las interacciones con otros agentes del sistema de innovación. El futuro de las exportaciones agropecuarias está comprometido por la creciente competencia internacional, por la vulnerabilidad de la producción agropecuaria a la aparición de nuevos problemas técnicos, por problemas en las estructuras de comercialización y por la debilidad del sistema nacional de innovación. El fortalecimiento del sistema de innovación requiere rediseñar los sistemas de investigación y extensión, para crear nuevas interacciones con otros agentes e introducir nuevos incentivos a los investigadores y administradores de la investigación.
Diffusion-limited aggregation with jumps and flights
Creators: name: Molchanov, Ilya
Publisher: name: arXiv
Year: 2006
Subjects: subject: Statistical Mechanics (cond-mat.stat-mech)
subject: Other Condensed Matter (cond-mat.other)
subject: FOS: Physical sciences

description: The paper suggests a generalisation of the diffusion-limited aggregation (DLA) based on using a general stochastic process to control particle movements before sticking to a growing cluster. This leads to models with variable characteristics that can provide a single framework for treating a number of earlier models of fractal growth: the DLA, the Eden model and the ballistic aggregation. Additionally, a classification of fractal growth models is suggested.
description: 13 pages, 7 figures
Quasirelativistic quasilocal finite wave-function collapse model
Creators: name: Pearle, Philip
Publisher: name: arXiv
Year: 2005
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: A Markovian wave function collapse model is presented where the collapse-inducing operator, constructed from quantum fields, is a manifestly covariant generalization of the mass density operator utilized in the nonrelativistic Continuous Spontaneous Localization (CSL) wave function collapse model. However, the model is not Lorentz invariant because two such operators do not commute at spacelike separation, i.e., the time-ordering operation in one Lorentz frame, the "preferred" frame, is not the time-ordering operation in another frame. However, the characteristic spacelike distance over which the commutator decays is the particle's Compton wavelength so, since the commutator rapidly gets quite small, the model is "almost" relativistic. This "QRCSL" model is completely finite: unlike previous, relativistic, models, it has no (infinite) energy production from the vacuum state. QRCSL calculations are given of the collapse rate for a single free particle in a superposition of spatially separated packets, and of the energy production rate for any number of free particles: these reduce to the CSL rates if the particle's Compton wavelength is small compared to the model's distance parameter. One motivation for QRCSL is the realization that previous relativistic models entail excitation of nuclear states which exceeds that of experiment, whereas QRCSL does not: an example is given involving quadrupole excitation of the $^{74}$Ge nucleus.
description: 10 pages, to be published in Phys. Rev. A
Maize Production and Agricultural Policies in Central America and Mexico
Creators: name: Sain, Gustavo
name: Lopez-Pereira, Miguel A.
name: Sain, Gustavo
name: Lopez-Pereira, Miguel A.
Publisher: name: Unknown
Year: 1999
Subjects: Agricultural and Food Policy
Crop Production/Industries

description: This paper reviews trends in maize production and consumption in Central America and Mexico in the context of the political and economic changes taking place in the region since the 1970s. The authors focus on the effects of the structural adjustment programs in the 1980s and 1990s. The analysis begins by reviewing the economic context in which maize production occurs in the region and the main economic policy instruments affecting the maize economy. Next, trends in maize consumption and production are analyzed, along with the main factors influencing maize production, including trends in the public financing of maize research and extension. The authors find that several factors related to structural adjustment have defined--and are still defining--the course of agriculture, including maize production, in the countries of the region. The impact of these factors on maize production, consumption, and import trends has been different in Central America and in Mexico. In particular, the reduction or complete elimination of production incentives, the reduction of trade barriers, the liberalization of input and product prices, the deregulation of the currency exchange rate, the control of inflation, and the restructuring of agricultural research systems between the public and the private sectors have determined how basic grains are produced in the region and how they will be produced in the future. Furthermore, the visible and increasing deterioration of the natural resource base has raised great concern about the need to promote more sustainable, environmentally friendly uses of production systems and natural resources.
Fermiology of Cuprates from First Principles: From Small Pockets to the Luttinger Fermi surface
Creators: name: Hozoi, L.
name: Laad, M. S.
name: Fulde, P.
Publisher: name: arXiv
Year: 2008
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: Superconductivity (cond-mat.supr-con)
subject: FOS: Physical sciences

description: Fermiology, the shape and size of the Fermi surface, underpins the low-temperature physical properties of a metal. Recent investigations of the Fermi surface of high-Tc superconductors, however, show a most unusual behavior: upon addition of carriers, ``Fermi'' pockets appear around nodal (hole doping) and antinodal (electron doping) regions of the Brillouin zone in the ``pseudogap'' state. With progressive doping, p, these evolve into well-defined Fermi surfaces around optimal doping (p_opt), with no pseudogap. Correspondingly, various physical responses, including d-wave superconductivity, evolve from highly anomalous, up to p_opt, to more conventional beyond. Describing this evolution holds the key to understanding high-temperature superconductivity. Here, we present ab initio quantum chemical results for cuprates, providing a quantitative description of the evolution of the Fermi surface with doping. Our results constitute an ab initio justification for several, hitherto proposed semiphenomenological theories, offering an unified basis for understanding of various, unusual physical responses of doped cuprates.
A quadratic Reynolds stress development for the turbulent Kolmogorov flow
Creators: name: Wu, Wenwei
name: Schmitt, Francois G.
name: Calzavarini, Enrico
name: Wang, Lipo
Publisher: name: arXiv
Year: 2021
Subjects: subject: Fluid Dynamics (physics.flu-dyn)
subject: Computational Physics (physics.comp-ph)
subject: FOS: Physical sciences
subject: physics.flu-dyn

description: We study the three-dimensional turbulent Kolmogorov flow, i.e. the Navier-Stokes equations forced by a low-single-wave-number sinusoidal force in a periodic domain, by means of direct numerical simulations. This classical model system is a realization of anisotropic and non-homogeneous hydrodynamic turbulence. Boussinesq's eddy viscosity linear relation is checked and found to be approximately valid over half of the system volume. A more general nonlinear quadratic Reynolds stress development is proposed and its parameters estimated at varying the Taylor scale-based Reynolds number in the flow up to the value 200. The case of a forcing with a different shape, here chosen Gaussian, is considered and the differences with the sinusoidal forcing are emphasized.
description: 11 pages
On utility maximization in discrete-time financial market models
Creators: name: Rasonyi, Miklos
name: Stettner, Lukasz
Publisher: name: arXiv
Year: 2005
Subjects: subject: Probability (math.PR)
subject: Computational Finance (q-fin.CP)
subject: FOS: Mathematics
subject: FOS: Economics and business
subject: 93E20, 91B28 (Primary) 91B16, 60G42. (Secondary)

description: We consider a discrete-time financial market model with finite time horizon and give conditions which guarantee the existence of an optimal strategy for the problem of maximizing expected terminal utility. Equivalent martingale measures are constructed using optimal strategies.
description: Published at http://dx.doi.org/10.1214/105051605000000089 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org)
Coherent control of population transfer between communicating defects
Creators: name: Weiss, Christoph
Publisher: name: arXiv
Year: 2006
Subjects: subject: Other Condensed Matter (cond-mat.other)
subject: FOS: Physical sciences

description: Population transfer between two identical, communicating defects in a one-dimensional tight-binding lattice can be systematically controlled by external time-periodic forcing. Employing a force with slowly changing amplitude, the time it takes to transfer a particle from one defect to the other can be altered over several orders of magnitude. An analytical expression is derived which shows how the forcing effectively changes the energy splitting between the defect states, and numerical model calculations illustrate the possibility of coherent control of the transfer.
description: 7 pages, 6 figures, to appear in Phys. Rev. B
Self-generated locality near a ferromagnetic quantum-critical point
Creators: name: Chubukov, Andrey V.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: We analyze the behavior of interacting fermions near a ferromagnetic Stoner instability. We show that the Landau damping of the spin susceptibility is a relevant perturbation near a ferromagnetic quantum-critical point (FQCP). We argue that, as the system approaches a FQCP, the fermionic self-energy crosses over from predominantly momentum dependent away from the transition to predominantly frequency dependent in the immediate vicinity of the transition. We argue that due to this self-generated locality, the quasiparticle effective mass does not diverge before a FQCP is reached.
description: 11 pages, & eps figures, submitted to PRB
Futuras fuentes de crecimiento de la productividad del trigo en la region del Bajío (Guanajuato, Mexico)
Creators: name: Aquino-Mercado, Pedro
name: Aquino-Mercado, Pedro
Publisher: name: Unknown
Year: 2003
Subjects: Crop Production/Industries

description: El objetivo de esta investigación es determinar la perspectiva de la producción de trigo en la región del Bajío (Guanajuato, México), como una zona estratégica para proveer la materia prima que requiere la industria molinera de la zona centro del país. Se determinó el comportamiento de los componentes de la producción mediante el cálculo de las tasas de crecimiento. Asimismo, se elaboró un diagnóstico de la situación actual de la productividad, para lo cual se realizó una encuesta en una muestra representativa de los productores de la región. Para determinar las fuentes de inestabilidad del ingreso del productor, se utilizó el análisis de medidas de variación (coeficientes de variación, varianzas y covarianzas). Se modeló una función de producción del tipo Cobb-Douglas para determinar los factores de la producción que están incidiendo en los niveles de productividad del cultivo de trigo. Para estimar la rentabilidad y competitividad actual del trigo, se elaboraron presupuestos de producción utilizando precios privados y precios económicos. También se llevó a cabo un análisis de sensibilidad para determinar la perspectiva del cultivo del trigo en la región. Los resultados obtenidos indican que los factores asociados a los niveles de rendimiento del trigo son la experiencia y la edad de los productores, el desvare, la nivelación, la fecha de siembra, el número de aplicaciones de fertilizante, el número de aplicaciones de insecticida, las dosis de nitrógeno y de fósforo, y el número de riegos. Los factores que inciden en detrimento de los niveles del rendimiento son las altas densidades de siembra y las altas dosis de fertilizante nitrogenado. Entre las prácticas de manejo que pueden mejorar la eficiencia en la aplicación de los insumos, se encuentran el desvare y la nivelación: el desvare al interactuar con la dosis de nitrógeno y la nivelación al interactuar con la aplicación de insecticidas, además del número de riegos con la dosis de nitrógeno y la aplicación de herbicida. La alta productividad de los sistemas de producción hace que la rentabilidad tanto financiera como económica de las tecnologías de producción de trigo analizadas sean positivas. Sin embargo, son muy sensibles a los cambios en los precios internacionales, la calidad del grano, el costo de los insumos, el tipo de cambio y las tecnologías de producción disponibles y potenciales.
Three active M dwarfs within 8 pc: L 449-1, L 43-72, & LP 949-15
Creators: name: Scholz, R. -D.
name: Curto, G. Lo
name: Méndez, R. A.
name: Hambaryan, V.
name: Costa, E.
name: Henry, T. J.
name: Schwope, A. D.
Publisher: name: arXiv
Year: 2005
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: Three nearby star candidates were selected as bright 2MASS point sources without associated optical sources, i.e. with potentially large proper motions, subsequently confirmed by multi-epoch optical data from the SuperCOSMOS Sky Surveys. All three objects are listed in the NLTT catalogue of high proper motion stars. Follow-up spectroscopic observations allowed us to classify L 449-1 as M4.0e dwarf at 5.7 pc, L43-72 as M4.5e dwarf at 7.2 pc, and LP 949-15 as M5.0e dwarf at 6.1 pc, using known absolute $JHK_\mathrm{s}$ magnitudes of dwarfs with corresponding spectral types, respectively. All three stars exhibit $Hα$ emission lines, and all three can be identified with bright X-ray sources. The available ROSAT light curves of two of the objects show typical flare-like variability. Thus, all three stars are active, very close potential neighbours of the Sun, previously not mentioned as such, certainly deserving further attention. In particular, these are very promising candidates for trigonometric parallax programs.
description: 4 pages, 3 figures, accepted for publication in Astronomy and Astrophysics
Integrals of Braided Hopf Algebras
Creators: name: Guo, Xijing
name: Zhang, Shouchuan
Publisher: name: arXiv
Year: 2005
Subjects: subject: Quantum Algebra (math.QA)
subject: Rings and Algebras (math.RA)
subject: FOS: Mathematics
subject: 16W30

description: The faithful quasi-dual $H^d$ and strict quasi-dual $H^{d'}$ of an infinite braided Hopf algebra $H$ are introduced and it is proved that every strict quasi-dual $H^{d'}$ is an $H$-Hopf module. The connection between the integrals and the maximal rational $H^{d}$-submodule $H^{d rat}$ of $H^{d}$ is found. That is, $H^{d rat}\cong \int ^l_{H^d} \otimes H$ is proved. The existence and uniqueness of integrals for braided Hopf algebras in the Yetter-Drinfeld category $(^B_B{\cal YD},C)$ are given.
description: 12
A Lorentz-violating SO(3) model: discussing the unitarity, causality and the 't Hooft-Polyakov monopoles
Creators: name: Scarpelli, A. P. Baeta
name: Helayel-Neto, J. A.
Publisher: name: arXiv
Year: 2006
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: In this paper, we extend the analysis of the Lorentz-violating Quantum Eletrodynamics to the non-Abelian case: an SO(3) Yang-Mills Lagrangian with the addition of the non-Abelian Chern-Simons-type term. We consider the spontaneous symmetry breaking of the model and inspect its spectrum in order to check if unitarity and causality are respected. An analysis of the topological structure is also carried out and we show that a 't Hooft-Polyakov solution for monopoles is still present.
description: 7 pages