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Biomedical subjects

A Latz

Publications and source records attributed to A Latz.

At least 19 recordsLinked to original sources
PubMed2004

AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+-dependent manner.

The Arabidopsis tandem-pore K(+) (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K(+) channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K(+) currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K(+) transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K(+) channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.

Animals↗
PubMed2002

Dynamical precursor of nematic order in a dense fluid of hard ellipsoids of revolution.

We investigate hard ellipsoids of revolution in a parameter regime where no long range nematic order is present but already finite-size domains are formed which show orientational order. Domain formation leads to a substantial slowing down of a collective rotational mode which separates well from the usual microscopic frequency regime. A dynamic coupling of this particular mode into all other modes provides a general mechanism which explains an excess peak in spectra of molecular fluids. Using molecular dynamics simulation on up to 4096 particles and on solving the molecular mode coupling equation we investigate dynamic properties of the peak and prove its orientational origin.

Journal Article↗
PubMed2001

Microscopic dynamics of molecular liquids and glasses: role of orientations and translation-rotation coupling.

We investigate the dynamics of a fluid of dipolar hard spheres in its liquid and glassy phases, with emphasis on the microscopic time or frequency regime. This system shows rather different glass transition scenarios related to its rich equilibrium behavior, which ranges from a simple hard sphere fluid to long range ferroelectric orientational order. In the liquid phase close to the ideal glass transition line and in the glassy regime a medium range orientational order occurs leading to a softening of an orientational mode. To investigate the role of this mode we use the molecular mode-coupling equations to calculate the spectra straight phi"lm(q,omega) and chi"lm(q,omega). In the center of mass spectra straight phi"00(q,omega) and chi"00(q,omega) we found, besides a high frequency peak at omega(hf), a peak at omega(op), about one decade below omega(hf) x omega(op) has almost no q dependence and exhibits an "isotope" effect omega(op) proportional to I(-1/2), with I the moment of inertia. We give evidence that the existence of this peak is related to the occurrence of medium range orientational order. It is shown that some of these features also exist for schematic mode coupling models.

Journal Article↗
PubMed2001

Light-scattering spectra of supercooled molecular liquids.

The light-scattering spectra of molecular liquids are derived within a generalized hydrodynamics. The wave-vector and scattering-angle dependencies are given in the most general case and the change of the spectral features from liquid to solidlike is discussed without phenomenological model assumptions for (general) dielectric systems without long-ranged order. Exact microscopic expressions are derived for the frequency dependent transport kernels, generalized thermodynamic derivatives, and the background spectra.

Journal Article↗
PubMed2000

Chaotic properties of dilute two- and three-dimensional random Lorentz gases. II. Open systems.

We calculate the spectrum of Lyapunov exponents for a point particle moving in a random array of fixed hard disk or hard sphere scatterers, i.e., the disordered Lorentz gas, in a generic nonequilibrium situation. In a large system which is finite in at least some directions, and with absorbing boundary conditions, the moving particle escapes the system with probability one. However, there is a set of zero Lebesgue measure of initial phase points for the moving particle, such that escape never occurs. Typically, this set of points forms a fractal repeller, and the Lyapunov spectrum is calculated here for trajectories on this repeller. For this calculation, we need the solution of the recently introduced extended Boltzmann equation for the nonequilibrium distribution of the radius of curvature matrix and the solution of the standard Boltzmann equation. The escape-rate formalism then gives an explicit result for the Kolmogorov Sinai entropy on the repeller.

Journal Article↗
PubMed2000

Test of molecular mode coupling theory for general rigid molecules

We report recent progress on the test of mode coupling theory for molecular liquids (MMCT) for molecules of arbitrary shape. The MMCT equations in the long time limit are solved for supercooled water including all molecular degrees of freedom. In contrast to our earlier treatment of water as a linear molecule, we find that the glass-transition temperature T(c) is overestimated by the theory as was found in the case of simple liquids. The nonergodicity parameters are calculated from the "full" set of MMCT equations truncated at l(co)=2. These results are compared (i) with the nonergodicity parameters from MMCT with l(co)=2 in the "dipole" approximation n=n(')=0 and the diagonalization approximation n=n(')=0, l=l(') and (ii) with the corresponding results from a MD simulation. This work supports the possibility that a reduction to the most prominent correlators may constitute a valid approximation for solving the MMCT equations for rigid molecules.

Journal Article↗
PubMed2000

Molecular correlations in a supercooled liquid

We present static and dynamic properties of molecular correlation functions S(lmn,l(')m(')n('))(q-->,t) in a simulated supercooled liquid of water molecules, as a preliminary effort in the direction of solving the molecular mode-coupling theory (MMCT) equations for supercooled molecular liquids. The temperature and time dependence of various molecular correlation functions, calculated from 250 ns long molecular dynamics simulations, show the characteristic patterns predicted by MMCT and shed light on the driving mechanism responsible for the slowing down of the molecular dynamics. We also discuss the symmetry properties of the molecular correlation functions that can be predicted on the basis of the C(2v) symmetry of the molecule. Analysis of the molecular dynamics results for the static correlators S(lmn,l(')m(')n('))(q-->) reveals that additional relationships between correlators with different signs of n and n(') exist. We prove that for molecules with C(rv) symmetry this unexpected result becomes exact at least for high temperatures.

Journal Article↗
PubMed2000

Ideal glass transitions for hard ellipsoids

For hard ellipsoids of revolution we calculate the phase diagram for the idealized glass transition. Our equations cover the glass physics in the full phase space, for all packing fractions and all aspect ratios X0. With increasing aspect ratio we find the idealized glass transition to become primarily driven by orientational degrees of freedom. For needlelike or platelike systems the transition is strongly influenced by a precursor of a nematic instability. We obtain three types of glass transition line. The first one (straight phi((B))(c)) corresponds to the conventional glass transition for spherical particles which is driven by the cage effect. At the second one (straight phi((B'))(c)), which occurs for rather nonspherical particles, a glass phase is formed that consists of domains. Within each domain there is a nematic order where the center of mass motion is quasiergodic, whereas the interdomain orientations build an orientational glass. The third glass transition line (straight phi((A))(c)) occurs for nearly spherical ellipsoids where the orientational degrees of freedom with odd parity, e.g., 180 degrees flips, freeze independently from the positions.

Journal Article↗
PubMed2000

Molecular mode-coupling theory applied to a liquid of diatomic molecules

We study the molecular mode-coupling theory for a liquid of diatomic molecules. The equations for the critical tensorial nonergodicity parameters F(m)(ll('))(q) and the critical amplitudes of the beta relaxation H(m)(ll('))(q) are solved up to a cutoff l(co)=2 without any further approximations. Here l,m are indices of spherical harmonics. Contrary to previous studies, where additional approximations were applied, we find in agreement with simulations that all molecular degrees of freedom vitrify at a single temperature T(c). The theoretical results for the nonergodicity parameters and the critical amplitudes are compared with those from simulations. The qualitative agreement is good for all molecular degrees of freedom. To study the influence of the cutoff on the nonergodicity parameter, we also calculate the nonergodicity parameters for an upper cutoff l(co)=4. In addition, we also propose a method for the calculation of the critical nonergodicity parameter from the liquid side of transition.

Journal Article↗
PubMed1999

Molecular mode-coupling theory for supercooled liquids: application to water.

We present mode-coupling equations for the description of the slow dynamics observed in supercooled molecular liquids close to the glass transition. The mode-coupling theory (MCT) originally formulated to study the slow relaxation in simple atomic liquids, and then extended to the analysis of liquids composed by linear molecules, is here generalized to systems of arbitrarily shaped, rigid molecules. We compare the predictions of the theory for the q-vector dependence of the molecular nonergodicity parameters, calculated by solving numerically the molecular MCT equations in two different approximation schemes, with "exact" results calculated from a molecular dynamics simulation of supercooled water. The agreement between theory and simulation data supports the view that MCT succeeds in describing the dynamics of supercooled molecular liquids, even for network forming ones.

Journal Article↗
PubMed1999

Fluids of hard ellipsoids: Phase diagram including a nematic instability from Percus-Yevick theory.

An important aspect of molecular fluids is the relation between orientation and translation parts of the two-particle correlations. Especially, a detailed knowledge of the influence of orientation correlations is needed to explain and calculate in detail the occurrence of a nematic phase. The simplest model system that shows both orientation and translation correlations is a system of hard ellipsoids. We investigate an isotropic fluid formed of hard ellipsoids with the Percus-Yevick theory. Solving the Percus-Yevick equations self-consistently and accurately in the high density regime gives, contrary to previous works, a clear criterion for a nematic instability. We calculate in detail the equilibrium phase diagram for a fluid of hard ellipsoids of revolution. Our results compare well with Monte Carlo simulations and density-functional theory.

Journal Article↗
PubMed1985

Adult outcomes of high-risk children: differential effects of town and kibbutz rearing.

We conducted a followup study 15 years after the initial examination of 46 of the Israeli children at risk for schizophrenia (index cases) and 44 of the control children. Thus, we were able to contact and examine 90 of the surviving 99 subjects of the investigation. Half of the subjects had grown up in the communal child-rearing setting of a kibbutz, and half had been raised by their own parents in cities in Israel. The kibbutz-index cases, at average age 25, show the highest incidence of psychiatric disorder. Environmental factors that may have led to this outcome are discussed.

Adult↗