829 research outputs found
Rotational isomerism about the 17(20)-bond of steroids and euphoids as shown by the crystal structures of euphol and tirucallol.
Effect of quantum fluctuations on structural phase transitions in SrTiO_3 and BaTiO_3
Using path-integral Monte Carol simulations and an ab initio effective
Hamiltonian, we study the effects of quantum fluctuations on structural phase
transitions in the cubic perovskite compounds SrTiO3 and BaTiO3. We find
quantum fluctuations affect ferroelectric (FE) transitions more strongly than
antiferrodistortive (AFD) ones, even though the effective mass of a single FE
local mode is larger. For SrTiO3 we find that the quantum fluctuations suppress
the FE transition completely, and reduce the AFD transition temperature from
130K to 110K. For BaTiO3, quantum fluctuations do not affect the order of the
transition, but do reduce the transition temperature by 35-50 K. The
implications of the calculations are discussed.Comment: Revtex (preprint style, 14 pages) + 2 postscript figures. A version
in two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#wz_qs
Stochastic model to assess bioeconomic impact of PRRS on pig farms in Costa Rica
Despite the economic importance of PRRS and its high prevalence in Costa Rica, there are no studies on the bioeconomic impact of the disease in the country or, even, in Central America. Such studies are essential in finding cost-effective preventive measures tailored for different production circumstances. Therefore, the objective of this study was to evaluate economic and production parameters of a PRRSV-infection for a medium-sized farrow-to-finish pig farm system in Costa Rica with a farm-level stochastic Monte Carlo simulation model. The effect of PRRS was assessed by scenario analysis, in which a baseline PRRS-free situation was compared against three alternative scenarios that assumed low, medium and high PRRS effects. The PRRS effects were based on data from local farms, scientific literature and expert opinion. Sensitivity analyses were performed to assess the impact of key input parameters on output variables. Results show that at the animal level, changes between the baseline and the PRRS-high scenario were estimated as: + 25 d in age to slaughter, - 9.9 pigs to slaughter (per breeding sow/yr), + 6% annual replacement rate, - 255 d in sow productive lifetime, - 6.9 mo in age at culling of sows, and + 24 non- productive days. For a medium size local farm (n = 588 sows), a reduction of 5826 fat pigs to slaughter per farm/yr from baseline compared to PRRS-high scenario was observed. PRRS-induced loss per farm per year was estimated at -US 180,109 and -US 2.63 for the baseline to US 77.1 per slaughtered pig/yr and US $892 per breeding sow/yr for the PRRS-high scenario. Results from the model indicate that pig farms with medium to high prevalence of PRRS will require optimal market conditions in order to have positive economic outcomes. These results can be helpful in the design of better control strategies for PRRS
Third order dielectric susceptibility in a model quantum paraelectric
In the context of perovskite quantum paraelectrics, we study the effects of a
quadrupolar interaction , in addition to the standard dipolar one .
We concentrate here on the nonlinear dielectric response , as
the main response function sensitive to quadrupolar (in our case
antiquadrupolar) interactions. We employ a 3D quantum four-state lattice model
and mean-field theory. The results show that inclusion of quadrupolar coupling
of moderate strength () is clearly accompanied by a
double change of sign of from negative to positive, near the
quantum temperature where the quantum paraelectric behaviour sets in. We
fit our to recent experimental data for SrTiO, where the
sign change is identified close to .Comment: 22 page
Determination of the Hurst Exponent by Use of Wavelet Transforms
We propose a new method for (global) Hurst exponent determination based on
wavelets. Using this method, we analyze synthetic data with predefined Hurst
exponents, fracture surfaces and data from economy. The results are compared
with those obtained from Fourier spectral analysis. When many samples are
available, the wavelet and Fourier methods are comparable in accuracy. However,
when one or only a few samples are available, the wavelet method outperforms
the Fourier method by a large margin.Comment: 10 pages RevTeX, 13 Postscript figures. Some additional material
compared to previous versio
Sterol 14α-Demethylase as a Potential Target for Antitrypanosomal Therapy: Enzyme Inhibition and Parasite Cell Growth
SummarySterol 14α-demethylases (CYP51) serve as primary targets for antifungal drugs, and specific inhibition of CYP51s in protozoan parasites Trypanosoma brucei (TB) and Trypanosoma cruzi (TC) might provide an effective treatment strategy for human trypanosomiases. Primary inhibitor selection is based initially on the cytochrome P450 spectral response to ligand binding. Ligands that demonstrate strongest binding parameters were examined as inhibitors of reconstituted TB and TC CYP51 activity in vitro. Direct correlation between potency of the compounds as CYP51 inhibitors and their antiparasitic effect in TB and TC cells implies essential requirements for endogenous sterol production in both trypanosomes and suggests a lead structure with a defined region most promising for further modifications. The approach developed here can be used for further large-scale search for new CYP51 inhibitors
Application of Global Positioning System and questionnaires data for the study of driver behavior on two-lane rural roads
This paper is a preprint of a paper accepted by IET Intelligent Transport Systems and is subject to Institution of Engineering and Technology Copyright. When the final version is published, the copy of record will be available at IET Digital LibraryMethodologies based on naturalistic observation provide the most accurate data for studying drivers' behaviour. This study presents a new methodology to obtain naturalistic data related to drivers' behaviour in a road segment. It is based on the combination of using global positioning system data and drivers' questionnaires. The continuous speed profiles along a road segment and the characteristics of drivers, of their trips and the type of their vehicles can be obtained for a great amount of drivers. It has already been successfully used for several studies, such as the development of models to estimate operating speed profile in two-lane rural road segments; or the characterisation of driving styles. These operating speed models have been the key for the development of a new geometric design consistency model, allowing an easier road safety evaluation. Besides, knowledge on the human factors that influence speed choice may be useful for road safety media campaigns and education programs designers, and also for the improvement of intelligent driver assistance systems.The authors thank 'Centre for Studies and Experimentation of Public Works (CEDEX)' of the 'Spanish Ministry of Public Works' that partially subsidizes the research. We also wish to thank to the 'General Directorate of Public Works, Urban Projects and Housing' of the 'Infrastructure, Territory and Environment Department' of the 'Valencian Government', to the 'Valencian Provincial Council' and to the 'General Directorate of Traffic' of the 'Ministry of the Interior' for their cooperation in field data gathering.Pérez Zuriaga, AM.; Camacho Torregrosa, FJ.; Campoy Ungria, JM.; García García, A. (2013). Application of Global Positioning System and questionnaires data for the study of driver behavior on two-lane rural roads. IET Intelligent Transport Systems. 7(2):182-189. doi:10.1049/iet-its.2012.0151S18218972Fourie, M., Walton, D., & Thomas, J. A. (2011). Naturalistic observation of drivers’ hands, speed and headway. Transportation Research Part F: Traffic Psychology and Behaviour, 14(5), 413-421. doi:10.1016/j.trf.2011.04.009Gibreel, G. M., Easa, S. M., & El-Dimeery, I. A. (2001). Prediction of Operating Speed on Three-Dimensional Highway Alignments. Journal of Transportation Engineering, 127(1), 21-30. doi:10.1061/(asce)0733-947x(2001)127:1(21)Fitzpatrick, K., & Collins, J. M. (2000). Speed-Profile Model for Two-Lane Rural Highways. Transportation Research Record: Journal of the Transportation Research Board, 1737(1), 42-49. doi:10.3141/1737-06Bella, F. (2008). Driving simulator for speed research on two-lane rural roads. Accident Analysis & Prevention, 40(3), 1078-1087. doi:10.1016/j.aap.2007.10.015Van Nes, N., Houtenbos, M., & Van Schagen, I. (2008). Improving speed behaviour: the potential of in-car speed assistance and speed limit credibility. IET Intelligent Transport Systems, 2(4), 323. doi:10.1049/iet-its:20080036Warner, H. W., & Åberg, L. (2006). Drivers’ decision to speed: A study inspired by the theory of planned behavior. Transportation Research Part F: Traffic Psychology and Behaviour, 9(6), 427-433. doi:10.1016/j.trf.2006.03.004Goldenbeld, C., & van Schagen, I. (2007). The credibility of speed limits on 80km/h rural roads: The effects of road and person(ality) characteristics. Accident Analysis & Prevention, 39(6), 1121-1130. doi:10.1016/j.aap.2007.02.012Zuriaga, A. M. P., García, A. G., Torregrosa, F. J. C., & D’Attoma, P. (2010). Modeling Operating Speed and Deceleration on Two-Lane Rural Roads with Global Positioning System Data. Transportation Research Record: Journal of the Transportation Research Board, 2171(1), 11-20. doi:10.3141/2171-02Ottesen, J. L., & Krammes, R. A. (2000). Speed-Profile Model for a Design-Consistency Evaluation Procedure in the United States. Transportation Research Record: Journal of the Transportation Research Board, 1701(1), 76-85. doi:10.3141/1701-10Park, P. Y., Miranda-Moreno, L. F., & Saccomanno, F. F. (2010). Estimation of speed differentials on rural highways using hierarchical linear regression models. Canadian Journal of Civil Engineering, 37(4), 624-637. doi:10.1139/l10-002Wasielewski, P. (1984). Speed as a measure of driver risk: Observed speeds versus driver and vehicle characteristics. Accident Analysis & Prevention, 16(2), 89-103. doi:10.1016/0001-4575(84)90034-4Williams, A. F., Kyrychenko, S. Y., & Retting, R. A. (2006). Characteristics of speeders. Journal of Safety Research, 37(3), 227-232. doi:10.1016/j.jsr.2006.04.001Lajunen, T., Karola, J., & Summala, H. (1997). Speed and Acceleration as Measures of Driving Style in Young Male Drivers. Perceptual and Motor Skills, 85(1), 3-16. doi:10.2466/pms.1997.85.1.3Af Wåhlberg, A. E. (2006). Speed choice versus celeration behavior as traffic accident predictor. Journal of Safety Research, 37(1), 43-51. doi:10.1016/j.jsr.2005.10.01
The skeletons of free distributive lattices
AbstractThe skeletons of free distributive lattices are studied by methods of formal concept analysis; in particular, a specific closure system of sublattices is elaborated to clarify the structure of the skeletons. Up to five generators, the skeletons are completely described
Towards defining reference materials for extracellular vesicle size, concentration, refractive index and epitope abundance
Accurate characterization of extracellular vesicles (EVs) is critical to
explore their diagnostic and therapeutic applications. As the EV research field
has developed, so too have the techniques used to characterize them. The
development of reference materials is required for the standardization of these
techniques. This work, initiated from the ISEV 2017 Biomarker Workshop in
Birmingham, UK, and with further discussion during the ISEV 2019
Standardization Workshop in Ghent, Belgium, sets out to elucidate which
reference materials are required and which are currently available to
standardize commonly used analysis platforms for characterizing EV size,
concentration, refractive index, and epitope expression. Due to their
predominant use, a particular focus is placed on the optical methods
nanoparticle tracking analysis and flow cytometry.Comment: 30 pages, 6 figures, 2 table
Regularity Properties and Pathologies of Position-Space Renormalization-Group Transformations
We reconsider the conceptual foundations of the renormalization-group (RG)
formalism, and prove some rigorous theorems on the regularity properties and
possible pathologies of the RG map. Regarding regularity, we show that the RG
map, defined on a suitable space of interactions (= formal Hamiltonians), is
always single-valued and Lipschitz continuous on its domain of definition. This
rules out a recently proposed scenario for the RG description of first-order
phase transitions. On the pathological side, we make rigorous some arguments of
Griffiths, Pearce and Israel, and prove in several cases that the renormalized
measure is not a Gibbs measure for any reasonable interaction. This means that
the RG map is ill-defined, and that the conventional RG description of
first-order phase transitions is not universally valid. For decimation or
Kadanoff transformations applied to the Ising model in dimension ,
these pathologies occur in a full neighborhood of the low-temperature part of the first-order
phase-transition surface. For block-averaging transformations applied to the
Ising model in dimension , the pathologies occur at low temperatures
for arbitrary magnetic-field strength. Pathologies may also occur in the
critical region for Ising models in dimension . We discuss in detail
the distinction between Gibbsian and non-Gibbsian measures, and give a rather
complete catalogue of the known examples. Finally, we discuss the heuristic and
numerical evidence on RG pathologies in the light of our rigorous theorems.Comment: 273 pages including 14 figures, Postscript, See also
ftp.scri.fsu.edu:hep-lat/papers/9210/9210032.ps.
- …