Anisotropy of the paramagnetic susceptibility in LaTiO3_{3}: The electron-distribution picture in the ground state

The energy-level scheme and wave functions of the titanium ions in LaTiO$_{3}$ are calculated using crystal-field theory and spin-orbit coupling. The theoretically derived temperature dependence and anisotropy of the magnetic susceptibility agree well with experimental data obtained in an untwinned single crystal. The refined fitting procedure reveals an almost isotropic molecular field and a temperature dependence of the van Vleck susceptibility. The charge distribution of the 3d--electron on the Ti positions and the principle values of the quadrupole moments are derived and agree with NMR data and recent measurements of orbital momentum $$ and crystal-field splitting. The low value of the ordered moment in the antiferromagnetic phase is discussed.Comment: 6 pages, 2 figures, 3 table

Evidence for Jahn-Teller distortions at the antiferromagnetic transition in LaTiO3_3

LaTiO$_3$ is known as Mott-insulator which orders antiferromagnetically at $T_{\rm N}=146$ K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At $T_{\rm N}$ significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc-resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.Comment: 4 pages, 4 figures; published in Phys. Rev. Lett. 91, 066403 (2003

Stochastic dynamics and control of a driven nonlinear spin chain: the role of Arnold diffusion

We study a chain of non-linear, interacting spins driven by a static and a time-dependent magnetic field. The aim is to identify the conditions for the locally and temporally controlled spin switching. Analytical and full numerical calculations show the possibility of stochastic control if the underlying semi-classical dynamics is chaotic. This is achievable by tuning the external field parameters according to the method described in this paper. We show analytically for a finite spin chain that Arnold diffusion is the underlying mechanism for the present stochastic control. Quantum mechanically we consider the regime where the classical dynamics is regular or chaotic. For the latter we utilize the random matrix theory. The efficiency and the stability of the non-equilibrium quantum spin-states are quantified by the time-dependence of the Bargmann angle related to the geometric phases of the states.Comment: Journal-ref: to appear in J.Phys.

Anisotropy paramagnetic susceptibility in LaTiO3

The energy-level scheme and wave functions of titanium ions in LaTiO 3 are calculated using crystal-field theory. The theoretically derived temperature dependence of the magnetic susceptibility agrees with our new experimental data obtained in an untwinned single crystal

Anisotropy of the paramagnetic susceptibility in LaTiO3: The electron-distribution picture in the ground state

The energy-level scheme and wave functions of the titanium ions in LaTiO3 are calculated using crystal-field theory and spin-orbit coupling. The theoretically derived temperature dependence and anisotropy of the magnetic susceptibility agree well with experimental data obtained in an untwinned single crystal. The refined fitting procedure reveals an almost isotropic molecular field and a temperature dependence of the van Vleck susceptibility. The charge distribution of the 3d-electron on the Ti positions and the principle values of the quadrupole moments are derived and agree with NMR data and recent measurements of orbital momentum 〈l〉 and crystal-field splitting. The low value of the ordered moment in the antiferromagnetic phase is discussed

Manifestation of the Arnol'd Diffusion in Quantum Systems

We study an analog of the classical Arnol'd diffusion in a quantum system of two coupled non-linear oscillators one of which is governed by an external periodic force with two frequencies. In the classical model this very weak diffusion happens in a narrow stochastic layer along the coupling resonance, and leads to an increase of total energy of the system. We show that the quantum dynamics of wave packets mimics, up to some extent, global properties of the classical Arnol'd diffusion. This specific diffusion represents a new type of quantum dynamics, and may be observed, for example, in 2D semiconductor structures (quantum billiards) perturbed by time-periodic external fields.Comment: RevTex, 4 pages including 7 ps-figures, corrected forma

Quantum Averaging I: Poincar\'e--von Zeipel is Rayleigh--Schr\"odinger

An exact analogue of the method of averaging in classical mechanics is constructed for self--adjoint operators. It is shown to be completely equivalent to the usual Rayleigh--Schr\"odinger perturbation theory but gives the sums over intermediate states in closed form expressions. The anharmonic oscillator and the Henon--Heiles system are treated as examples to illustrate the quantum averaging method.Comment: 12 pages, LaTeX, to appear in Journ. Phys.

Cellular and humoral immune responses and protection against schistosomes induced by a radiation-attenuated vaccine in chimpanzees

The radiation-attenuated Schistosoma mansoni vaccine is highly effective in rodents and primates but has never been tested in humans, primarily for safety reasons. To strengthen its status as a paradigm for a human recombinant antigen vaccine, we have undertaken a small-scale vaccination and challenge experiment in chimpanzees (Pan troglodytes). Immunological, clinical, and parasitological parameters were measured in three animals after multiple vaccinations, together with three controls, during the acute and chronic stages of challenge infection up to chemotherapeutic cure. Vaccination induced a strong in vitro proliferative response and early gamma interferon production, but type 2 cytokines were dominant by the time of challenge. The controls showed little response to challenge infection before the acute stage of the disease, initiated by egg deposition. In contrast, the responses of vaccinated animals were muted throughout the challenge period. Vaccination also induced parasite-specific immunoglobulin M (IgM) and IgG, which reached high levels at the time of challenge, while in control animals levels did not rise markedly before egg deposition. The protective effects of vaccination were manifested as an amelioration of acute disease and overall morbidity, revealed by differences in gamma-glutamyl transferase level, leukocytosis, eosinophilia, and hematocrit. Moreover, vaccinated chimpanzees had a 46% lower level of circulating cathodic antigen and a 38% reduction in fecal egg output, compared to controls, during the chronic phase of infection

Lack of Evidence for the Direct Activation of Endothelial Cells by Adult Female and Microfilarial Excretory-Secretory Products

Lymphangiectasia (dilation of the lymphatic vessel (LV)) is pathognomonic for lymphatic filariasis. In both infected humans and animal models of infection, lymphangiectasia is not restricted to the site of the worm nest, but is found along the infected vessel. These observations argue that soluble products secreted by the worm could be mediating this effect by activating the lymphatic endothelial cells (LEC) lining the vessel. We tested the ability of filarial Excretory-Secretory products to activate LECs, but were unable to detect a direct effect of the Excretory-Secretory products on the activation of LEC as assessed by a variety of approaches including cellular proliferation, cell surface molecule expression and cytokine and growth factor production (although other mediators used as positive controls did induce these effects). Collectively, these results do not support the hypothesis that Excretory-Secretory products directly activate LECs

Predicting Cell Cycle Regulated Genes by Causal Interactions

The fundamental difference between classic and modern biology is that technological innovations allow to generate high-throughput data to get insights into molecular interactions on a genomic scale. These high-throughput data can be used to infer gene networks, e.g., the transcriptional regulatory or signaling network, representing a blue print of the current dynamical state of the cellular system. However, gene networks do not provide direct answers to biological questions, instead, they need to be analyzed to reveal functional information of molecular working mechanisms. In this paper we propose a new approach to analyze the transcriptional regulatory network of yeast to predict cell cycle regulated genes. The novelty of our approach is that, in contrast to all other approaches aiming to predict cell cycle regulated genes, we do not use time series data but base our analysis on the prior information of causal interactions among genes. The major purpose of the present paper is to predict cell cycle regulated genes in S. cerevisiae. Our analysis is based on the transcriptional regulatory network, representing causal interactions between genes, and a list of known periodic genes. No further data are used. Our approach utilizes the causal membership of genes and the hierarchical organization of the transcriptional regulatory network leading to two groups of periodic genes with a well defined direction of information flow. We predict genes as periodic if they appear on unique shortest paths connecting two periodic genes from different hierarchy levels. Our results demonstrate that a classical problem as the prediction of cell cycle regulated genes can be seen in a new light if the concept of a causal membership of a gene is applied consequently. This also shows that there is a wealth of information buried in the transcriptional regulatory network whose unraveling may require more elaborate concepts than it might seem at first