Critical properties of the XXZ model with long-range interactions on the double chain

The $XXZ$ model $(s = 1/2)$ in a transverse field on a double chain with a uniform long-range interaction among the $z$ components of the spins is considered. The nearest-neighbour interactions are restricted to the components in the $xy$ plane and to the spins within the same chain leg, such that the Hamiltonian is given by $H = -\sum_{m=1}^{2} J_{m} \sum_{j=1}^{N}(S_{m,j}^{x}S_{m, j+1}^{x} + S_{m,j}^{y}S_{m,j+1}^{y}) - \frac{I}{N}\sum_{m,n=1}^{2} \sum_{j,k=1}^{N}S_{m,j}^{z}S_{n,k}^{z}-h\sum_{m=1}^{2} \sum_{j=1}^{N}S_{m,j}^{z}$, where $N$ is the number of sites of the lattice and $m,n$ $(m,n = 1, 2)$ label the chain legs. The model is solved exactly by introducing the Jordan-Wigner and integral Gaussian transformations, which map the Hamiltonian in a non-interacting fermion system and corresponds to an extension of the model recently studied by the authors for a single chain. The equation of state is obtained in closed form, and the critical classical (at $T > 0$) and quantum (at $T = 0$) behaviours can be determined exactly. The quantum critical surface is determined in the space generated by the transverse field and interaction parameters, and the crossover lines separating the different critical regimes are also obtained. It is also shown that, differently from the results obtained for the single chain, the system can present multiple quantum transitions.Comment: 02 pages, 02 figures, to appear in JMMM (Proceedings of ICM2006

The XY model on the one-dimensional superlattice: static properties

The XY model (s=1/2) on the one-dimensional alternating superlattice (closed chain) is solved exactly by using a generalized Jordan-Wigner transformation and the Green function method. Closed expressions are obtained for the excitation spectrum, the internal energy, the specific heat, the average magnetization per site, the static transverse susceptibility and the two-spin correlation function in the field direction at arbitrary temperature. At T=0 it is shown that the system presents multiple second order phase transitions induced by the transverse field, which are associated to the zero energy mode with wave number equal to 0 or $\pi$. It is also shown that the average magnetization as a function of the field presents, alternately, regions of plateaux (disordered phases) and regions of variable magnetization (ordered phases). The static correlation function presents an oscillating behaviour in the ordered phase and its period goes to infinity at the critical point.Comment: 16 pages, 16 figure

Friedel oscillations in one-dimensional metals: from Luttinger's theorem to the Luttinger liquid

Charge density and magnetization density profiles of one-dimensional metals are investigated by two complementary many-body methods: numerically exact (Lanczos) diagonalization, and the Bethe-Ansatz local-density approximation with and without a simple self-interaction correction. Depending on the magnetization of the system, local approximations reproduce different Fourier components of the exact Friedel oscillations.Comment: 3 pages, 3 figures, Manuscript accepted by Journal of Magnetism and Magnetic Materials, special issue for LAWMMM 2007 conferenc

Effect of particle size distribution and dynamics on the performance of two-dimensional packing

AbstractExtensive computer simulation is used to revisit and to generalize two classical problems: (i) the random car-parking dynamics of A. Rényi and (ii) the irreversible random sequential adsorption (RSA) of parallel squares of same size on a planar substrate of area L2. In this paper, differently from the classical RSA, the squares obey the size distribution n(a)=n(1)a−τ, where a=1,2,3,… is the area of the squares. Using this scaling distribution and three classes of packing dynamics we study the final packing fraction of particles, ⊖(τ,L), and in particular its thermodynamic limit L→∞. We show that the efficiency to attain a high/low packing density of particles on the substrate is strongly dependent on the value of the exponent τ and on the characteristics of the dynamics

Aportaciones desde la biomecánica de la natación de competición

A natação é uma modalidade individual, cíclica e fechada, pelo que, no respectivo quadro de factores determinantes do sucesso competitivo, a optimização do gesto técnico desempenha um papel determinante.info:eu-repo/semantics/publishedVersio

Relationships between energy cost, swimming velocity and speed fluctuation in elite butterfliers

In swimming science, economy of movement is an interesting field of research. Several investigations have been conducted to understand the role of bioenergetical profile to performance. Most of those studies focused exclusively on the contribution of The individual correlations between E-tot and v ranged from R=0.95 aerobic system to produce energy for movement, even though all competitive swimming events also require significant (p=0.05) to R=0.90 (p<0.01). For pooled data the relationship was contribution from anaerobic energetic system to cover total energy expenditure. R=0.70 (p<0.01). The individual correlations between EC and d

Molecular cloning and biochemical characterization of a Cu,Zn-superoxide dismutase from Scedosporium apiospermum.

A Cu,Zn-superoxide dismutase has been characterized from Scedosporium apiospermum, a fungus which often colonizes the respiratory tract of patients with cystic fibrosis. Enzyme production was stimulated by iron starvation. Purification was achieved from mycelial extract from 7-day-old cultures on Amberlite XAD-16. The purified enzyme presented a relative molecular mass of 16.4 kDa under reducing conditions and was inhibited by potassium cyanide and diethyldithiocarbamate, which are two known inhibitors of Cu,Zn-SODs. Its optimum pH was 7.0 and the enzyme retained full activity after pretreatment at temperatures up to 50 degrees C. Moreover, a 450-bp fragment of the gene encoding the enzyme was amplified by PCR using degenerate primers designed from sequence alignment of four fungal Cu,Zn-SODs. Sequence data from this fragment allowed us to design primers which were used to amplify by walking-PCR the flanking regions of the known fragment. SaSODC gene (890 bp) corresponded to a 154 amino acid polypeptide with a predicted molecular mass of 15.9 kDa. A database search for sequence homology revealed for the deduced amino acid sequence 72 and 83% identity rate with Cu,Zn-SODs from Aspergillus fumigatus and Neurospora crassa, respectively. To our knowledge, this enzyme is the first putative virulence factor of S. apiospermum to be characterized

Energy cost and intracyclic variation of the velocity of the centre of mass in butterfly stroke

The purpose of this study was to examine the relationship between the intra-cycle variation of the horizontal velocity of displacement (dV) and the energy cost (EC) in butterfly stroke. Five Portuguese national level swimmers performed one maximal and two submaximal 200-m butterfly swims. The oxygen consumption was measured breath-by-breath by portable metabolic cart. A respiratory snorkel and valve system with low hydrodynamic resistance was used to measure pulmonary ventilation and to collect breathing air samples. Blood samples from the ear lobe were collected before and after each swim to analyse blood lactate concentration. Total energy expenditure (Etot) and EC were calculated for each swim. The swims were videotaped in the sagittal plane with a set of two cameras providing dual projection from both underwater and above the water surface. The APAS system was used to analyse dV for the centre of mass. The Etot increased linearly with the increasing V, presenting a significant correlation coefficient between these parameters (r=0.827, P<0.001). The increase in EC was significantly associated with the increase in the dV (r=0.807, P<0.001). All data were presented as the mean value and the standard deviation. It is concluded that high intra-cycle variation of the velocity of the centre of mass was related to less efficient swimming and vice versa for the butterfly stroke

Unraveling the simultaneous shock magnetization and demagnetization of rocks

International audienceIn the natural case of an hypervelocity impact on a planetary or asteroidal surface, two competing phenomena occur: partial or complete shock demagnetization of pre-existing remanence and acquisition of shock remanent magnetization (SRM). In this paper, to better understand the effects of shock on the magnetic history of rocks, we simulate this natural case through laser shock experiments in controlled magnetic field. As previously shown, SRM is strictly proportional to the ambient field at the time of impact and parallel to the ambient field. Moreover, there is no directional or intensity heterogeneity of the SRM down to the scale of ∼0.2mm. We also show that the intensity of SRM is independent of the initial remanence state of the rock. Shock demagnetization and magnetization appear to be distinct phenomena that do not necessarily affect identical populations of grains. As such, shock demagnetization is not a limiting case of shock magnetization in zero field

Desperdício alimentar e satisfação do consumidor com o serviço de alimentação da Escola de Hotelaria e Turismo de Coimbra, Portugal

Introdução: O desperdício alimentar é matéria de interesse para os serviços de alimentação escolares. Uma das causas apontadas para sua ocorrência é a falta de consciência, por parte dos consumidores, para este problema. Objetivo: Avaliar o desperdício de alimentos nas refeições servidas no refeitório, a perceção dos consumidores em relação ao mesmo e sua satisfação com o serviço de alimentação. Metodologia: Foram avaliadas dois almoços, em dias consecutivos. As sobras e os restos resultantes da refeição foram pesados por componentes da mesma. Consideram-se inaceitáveis valores de desperdício superiores a 10%. As variáveis restantes foram avaliadas através da aplicação de um questionário aos utentes. Resultados e Discussão: A maioria dos indivíduos referiu estar satisfeita com o serviço de alimentação. Observaram-se 22,7% de sobras e 12,7% de restos, em média, nas refeições avaliadas. O componente do prato com maior quantidade de restos foi o peixe (25,37%), muito superior à carne (14,15%). Um valor superior a 20% de sobras foi encontrado para todos os componentes da refeição, exceto para o componente proteico e para o pão. Os inquiridos identificaram o fornecedor de hidratos de carbono como o componente mais desperdiçado, e referiram que normalmente não desperdiçam alimentos ao almoço. Conclusões: Apesar da satisfação com o serviço de refeições, os resultados do desperdício alimentar são considerados inaceitáveis e refletem a necessidade de melhorar o planeamento das refeições e a adequação das ementas às preferências dos consumidores. A dissociação entre a perceção de desperdício de alimentos e da quantidade e tipo de alimentos efetivamente desperdiçado justifica a intervenção ao nível da sensibilização dos usuários de cafeteria, como possível estratégia para reduzir o desperdício.Introduction: Food waste is a matter of concern in school foodservices. One of the causes given for its occurrence is the lackof awareness of consumers for food waste problem. Objective:Assess food waste of meals served at the cafeteria, the perceptionof consumers in relation to their own food waste and theirsatisfaction with the food service. Methodology: There wereassessed lunch meals, in two consecutive days. The leftoversand plate waste resulting from school lunch were weighed bymeal components. It was considered that values above 10% ofleftovers and plate waste were unacceptable. Other variableswere assessed through a questionnaire applied to consumers.Results and Discussion: Most respondents were satisfied with foodservice. It was found 22.7% of leftovers and 12.7% of plate wasteas average on the meals evaluated. The main dish componentwith highest amount of plate waste was fish (25.37%), muchhigher than meat (14.15%). An amount above 20% leftovers wasfound for all components, except for protein source and bread.There was a dissociation between the perception of wasted foodand actual plate waste. Conclusions: In spite of satisfaction ofconsumers with food service, the results of food waste found areconsidered unacceptable and reflect the need to improve theplanning of meals and menus adequacy to consumer preferences,as well as to develop strategies to reduce meals rejection. Thedissociation between perception of food waste and the amountand type of food effectively wasted, justify the intervention atthe level of awareness of users of cafeteria, as a possible strategyto reduce waste.Key words: Food Waste. Food Services. Consumer Satisfactio