1,637 research outputs found
Quantum density anomaly in optically trapped ultracold gases
We show that the Bose-Hubbard Model exhibits an increase in density with
temperature at fixed pressure in the regular fluid regime and in the superfluid
phase. The anomaly at the Bose-Einstein condensate is the first density anomaly
observed in a quantum state. We propose that the mechanism underlying both the
normal phase and the superfluid phase anomalies is related to zero point
entropies and ground state phase transitions. A connection with the typical
experimental scales and setups is also addressed. This key finding opens a new
pathway for theoretical and experimental studies of water-like anomalies in the
area of ultracold quantum gases
Waterlike density anomaly in fermions
In this work we explore the one-dimensional extended Hubbard model as a fluid
system modelling liquid phases of different densities. This model naturally
displays two length scales of interaction, which are connected with waterlike
anomalies. We analyze the density anomaly as a function of the model
parameters, namely the hopping, on-site and first neighbor interactions. We
show that this anomaly is present for a wide range of model parameters and is
connected to a ground-state liquid-liquid critical point.Comment: 15 pages, 9 figure
Liquid crystal phase and waterlike anomalies in a core-softened shoulder-dumbbells system
Using molecular dynamics we investigate the thermodynamics, dynamics and
structure of 250 diatomic molecules interacting by a core-softened potential.
This system exhibits thermodynamics, dynamics and structural anomalies: a
maximum in density-temperature plane at constante pressure and maximum and
minimum points in the diffusivity and translational order parameter against
density at constant temperature. Starting with very dense systems and
decreasing density the mobility at low temperatures first increases, reach a
maximum, then decreases, reach a minimum and finally increases. In the
pressure-temperature phase diagram the line of maximum translational order
parameter is located outside the line of diffusivity extrema that is enclosing
the temperature of maximum density line. We compare our results with the
monomeric system showing that the anisotropy due to the dumbbell leads to a
much larger solid phase and to the appearance of a liquid crystal phase. the
double ranged thermodynamic and dynamic anomalies.Comment: 14 pages, 5 figure
Configuration space partitioning in tilings of a bounded region of the plane
Given a finite collection of two-dimensional tile types, the field of study
concerned with covering the plane with tiles of these types exclusively has a
long history, having enjoyed great prominence in the last six to seven decades.
Much of this interest has revolved around fundamental geometrical problems such
as minimizing the variety of tile types to be used, and also around important
applications in areas such as crystallography as well as others. All these
applications are of course confined to finite spatial regions, but in many
cases they refer back directly to progress in tiling the whole, unbounded
plane. Tilings of bounded regions of the plane have also been actively studied,
but in general the additional complications imposed by the boundary conditions
tend to constrain progress to mostly indirect results, such as recurrence
relations. Here we study the tiling of rectangular regions of the plane by
rectangular tiles. The tile types we use are squares, dominoes, and straight
tetraminoes. For this set of tile types, not even recurrence relations seem to
be available. Our approach is to seek to characterize this complex system
through some fundamental physical quantities. We do this on two parallel
tracks, one analytical for what seems to be the most complex special case still
amenable to such approach, the other based on the Wang-Landau method for
state-density estimation. Given a simple energy function based solely on tile
contacts, we have found either approach to lead to illuminating depictions of
entropy, temperature, and above all partitions of the configuration space. The
notion of a configuration, in this context, refers to how many tiles of each
type are used. We have found that certain partitions help bind together
different aspects of the system in question and conjecture that future
applications will benefit from the possibilities they afford.Comment: This version includes minor fixes and a new table, and updates
metadat
Stress-strain behavior of concrete block masonry prisms under compression
The aim of this work is to critically assess a stress-strain model using experimental masonry
prisms constructed from different blocks and mortar. The following conclusion may be drawn
from this work: mortar is mostly responsible for the non-linear behavior of masonry. The
initial tangent modulus, obtained taking into account the compressive strength, provides a
strongly non-linear relationship between elasticity modulus and compressive strength
Produção e tamanho de grãos de café (Coffea arabica L.) cv Catuaí em diferentes arranjos populacionais e disponibilidades de água no solo
The purpose of this research was to evaluate the effect of drip irrigation under different population arrangements on the phytometric features, coffee productivity and bean size classification according to sieve retention. The experiment with Coffea arabica L. cv Catuaí was carried out in Mococa, São Paulo, Brazil. The experimental design was a 6 x 2 factorial scheme in randomized blocks, with four replications. The six densities of plantation were E1 (1.60 x 0.50 m); E2 (1.60 x 0.75 m); E3 (1.60 x 1.00 m); E4 (3.20 x 0.50 m); E5 (3.20 x 0.75 m) and E6 (3.20 x 1.00 m), which were divided according to the availability of water (irrigated - I - or non-irrigated - NI - groups). Data were submitted to analysis of variance and averages compared by Tukey test at 1 and 5% of probability. Descriptive analysis of coffee beans according to sieve classification was performed. Irrigation promoted an increase in plant height, crown diameter and production of processed coffee when compared with the NI group. Interaction between population arrangement and irrigation was observed, with an increase in production and crown diameter as the spacing was decreased. Therefore, irrigation provided significant increase in coffee bean size.O objetivo deste estudo foi avaliar o efeito da irrigação por gotejamento em diferentes arranjos populacionais nas características fitométricas, na produtividade de café beneficiado e na classificação dos grãos por tamanho, de acordo com a retenção em peneiras. O experimento foi conduzido em Mococa-SP, com o cafeeiro Coffea arabica L. cv Catuaí. Adotou-se o delineamento experimental em blocos ao acaso, em esquema fatorial 6 x 2, com quatro repetições, sendo seis densidades de plantio: E1 (1,60 x 0,50 m); E2 (1,60 x 0,75 m); E3 (1,60 x 1,00 m); E4 (3,20 x 0,50 m); E5 (3,20 x 0,75 m), e E6 (3,20 x 1,00 m), divididas em irrigadas (I) e não irrigadas (NI). As variáveis foram submetidas à análise de variância, e as médias, comparadas entre si pelo teste de Tukey, a 1 e 5% de probabilidade. Foi realizada análise descritiva dos grãos nas classes de peneiras. A irrigação promoveu aumento na altura das plantas, maior diâmetro de copa e produção de café beneficiado quando comparado ao sistema não irrigado. Houve interação entre arranjo populacional e irrigação, com aumento na produção e no diâmetro da copa, conforme o espaçamento era reduzido. O uso da irrigação propiciou aumentos significativos na granulometria dos grãos de café.14515
Pt-Decorated TiO2 Materials Supported on Carbon : Increasing Activities and Stabilities toward the ORR by Tuning the Pt Loading
Pt nanoparticles (Pt NPs) supported on carbon have been widely employed as electrocatalysts toward oxygen reduction reaction. The development of more efficient electrocatalysts that enable one to reduce or even not require the use of Pt is a central challenge. In addition to the control over the physical and chemical features of Pt NPs, metal support interactions can be employed to enhance activities via the generation and exposure of surface-active sites. In this context, we report herein the development of electrocatalysts composed of Pt NPs supported on TiO2 microspheres, that were subsequently impregnated onto carbon. We have found that, by optimizing the loading of Pt at the TiO2 surface, the electrocatalytic activity toward the ORR could be improved compared to that of the commercial Pt/C (E-TEK) material, even at lower Pt loadings. The enhancement in activities could be assigned to the balance between Pt loading and generation of reactive surface sites, such as adsorbed oxygenated species. Moreover, the utilization of TiO2 as support enabled improved stabilities relative to Pt/C (E-TEK). We believe that the results described herein may inspire the development of electrocatalysts for the ORR with improved activities and stabilities.Peer reviewe
Water regimes and bean cultivar effects on the soil porous system characteristics
Bean (Phaseolus vulgaris L.) is a crop of great economic and social impacts in Brazil. This crop is extremely appreciated by the Brazilian population and an important source of protein. Usually the small farmers are responsible by the largest production of the bean in Brazil. This work deals with the analysis of the effect of different water regimes (35, 28, 21 and 14%) on the porous system of a soil cropped with two distinct cultivars (Campos Gerais and Tuiuiú). Soil water retention curve (SWRC) and its derivative were utilized with the aim of investigating the changes in the porous system. Pore size distribution was also evaluated. The experiment was carried out at a greenhouse and the soil water content for the different water regimes was monitored by means of a TDR. Four undisturbed samples were collected from each wooden bed (eight) for the physic-hydrical characterization. Discrepancies in the SWRC were noticed for the region of small pressure heads. Differences were not observed between bean cultivars to SWRC. However, the water capacity function was sensitive to show differences in the soil porous system due to the treatments and cultivars. The lowest water regimes promoted the highest volume of fissures (big pores >250 µm) and, consequently, the highest ones had the largest volume of storage pores (<25 µm)
Trigger efficiencies of a proposed beam monitoring detector (BeBe) for p+p collisions at NICA energies
The Multipurpose Detector (MPD) consists of a typical array of sub-detectors
to study the nuclear matter originating from the collisions of beams provided
by the Nuclotron-based Ion Collider fAcility (NICA). A beam monitoring
detector~(BeBe) is proposed for stage 2 of MPD to increase the trigger
capabilities. BeBe is constituted of two plastic scintillator disks segmented
in 80 cells away from the interaction point of MPD. Laboratory
measurements to obtain the energy resolution of an individual BeBe cell
prototype are presented. It is shown that an energy resolution of
can be obtained. Based on Monte Carlo simulations, the trigger efficiencies of
the BeBe are presented for p+p collisions at 11~GeV considering a threshold in
the energy loss of the charged particles reaching the detector
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