Lieb-Liniger-like model of quantum solvation in CO-(4)HeN clusters.

Small (4)He clusters doped with various molecules allow for the study of "quantum solvation" as a function of cluster size. A peculiarity of quantum solvation is that, as the number of (4)He atoms is increased from N = 1, the solvent appears to decouple from the molecule which, in turn, appears to undergo free rotation. This is generally taken to signify the onset of "microscopic superfluidity." Currently, little is known about the quantum mechanics of the decoupling mechanism, mainly because the system is a quantum (N + 1)-body problem in three dimensions which makes computations difficult. Here, a one-dimensional model is studied in which the (4)He atoms are confined to revolve on a ring and encircle a rotating CO molecule. The Lanczos algorithm is used to investigate the eigenvalue spectrum as the number of (4)He atoms is varied. Substantial solvent decoupling is observed for as few as N = 5 (4)He atoms. Examination of the Hamiltonian matrix, which has an almost block diagonal structure, reveals increasingly weak inter-block (solvent-molecule) coupling as the number of (4)He atoms is increased. In the absence of a dopant molecule the system is similar to a Lieb-Liniger (LL) gas and we find a relatively rapid transition to the LL limit as N is increased. In essence, the molecule initially-for very small N-provides a central, if relatively weak, attraction to organize the cluster; as more (4)He atoms are added, the repulsive interactions between the identical bosons start to dominate as the solvation ring (shell) becomes more crowded which causes the molecule to start to decouple. For low N, the molecule pins the atoms in place relative to itself; as N increases the atom-atom repulsion starts to dominate the Hamiltonian and the molecule decouples. We conclude that, while the notion of superfluidity is a useful and correct description of the decoupling process, a molecular viewpoint provides complementary insights into the quantum mechanism of the transition from a molecular cluster to a quantum solvated molecule.

Celestial mechanics on a microscopic scale.

Classical and semiclassical methods are unrivaled in providing an intuitive and computationally tractable approach to the study of atomic, molecular, and nuclear dynamics. An important advantage of such methods is their ability to uncover in a single picture underlying structures that may be hard to extract from the profusion of data supplied by detailed quantum calculations. Modern trends in semiclassical mechanics are described, particularly the combination of group theoretical methods with techniques of nonlinear dynamics. Application is made to intramolecular energy transfer and to the electronic structure of atomic Rydberg states in external electric and magnetic fields.

Expression of human hepatic glucokinase in transgenic mice liver results in decreased glucose levels and reduced body weight.

Glucokinase is the predominant hexokinase in pancreatic beta-cells and liver parenchymal cells and functions as a critical component of the glucose-sensing apparatus in these glucose-responsive cell types. In the beta-cells, the sensing leads to insulin secretion, while the role in hepatocytes is thought to be in hepatic glucose uptake. To determine the physiological response to an increase in hepatic glucokinase expression, transgenic mice expressing the human hepatic glucokinase gene under the control of a liver-specific human apolipoprotein A-I gene enhancer were generated. Transgenic mice had twofold higher total fasting hepatic glucokinase mRNA, which resulted in a modest 20% increase in fasting glucokinase activity. These animals showed lower fasting plasma glucose, insulin, and lactate levels and improved tolerance to glucose. In addition, glucokinase transgenic animals weighed less and had lower BMI than nontransgenic animals. Thus, glucokinase transgenic animals demonstrate that a modest change in hepatic glucokinase activity enhances the metabolism of glucose.

A Saturnian atom.

In Bohr's original planetary model of the atom the electron moves along orbits of special geometric simplicity. While wave mechanics precludes the idea that a physical path could be ascribed to the electron, a classical or planetary atom can still be envisaged in which the electronic wavepacket neither spreads nor disperses as its center moves along the Kepler orbit, and this orbit is conned to a single plane in space. We show theoretically how an electronic wavepacket may be localized in this fashion in a similar way to ion confinement in a Penning trap. Because external fields are needed to keep the packet confined, a more fitting analogy than a planetary orbit is the motion of a charged dust grain in one of the rings of a giant planet such as Saturn.

Transition state theory without time-reversal symmetry: chaotic ionization of the hydrogen atom

We present the first application of transition state theory to a system that evolves from an initial to a final state without time-reversal symmetry. The problem studied is the chaotic ionization of a hydrogen atom in crossed electric and magnetic fields. The stable manifolds of the transition state reveal a fractal tiling which connects the geometrical properties of the tiling to the ionization rate, leading to a theoretical explanation for the computational and experimental observation of "prompt" and "delayed" electrons in this problem.

Stabilization of molecular atoms

We demonstrate the possibility of stabilizing the motion of ion-pair states through the use of external electric and magnetic fields. In conjunction with the Coulomb force, these fields can be engineered so as to lead to the creation of outer equilibrium points which can support non-spreading coherent wavepackets and long-lived states. Specific application is made to the H(+)-H- ion pair, recently investigated using threshold ion-pair production spectroscopy (TIPPS).

Mice mutant for glucokinase regulatory protein exhibit decreased liver glucokinase: a sequestration mechanism in metabolic regulation.

The importance of glucokinase (GK; EC 2.7.1.12) in glucose homeostasis has been demonstrated by the association of GK mutations with diabetes mellitus in humans and by alterations in glucose metabolism in transgenic and gene knockout mice. Liver GK activity in humans and rodents is allosterically inhibited by GK regulatory protein (GKRP). To further understand the role of GKRP in GK regulation, the mouse GKRP gene was inactivated. With the knockout of the GKRP gene, there was a parallel loss of GK protein and activity in mutant mouse liver. The loss was primarily because of posttranscriptional regulation of GK, indicating a positive regulatory role for GKRP in maintaining GK levels and activity. As in rat hepatocytes, both GK and GKRP were localized in the nuclei of mouse hepatocytes cultured in low-glucose-containing medium. In the presence of fructose or high concentrations of glucose, conditions known to relieve GK inhibition by GKRP in vitro, only GK was translocated into the cytoplasm. In the GKRP-mutant hepatocytes, GK was not found in the nucleus under any tested conditions. We propose that GKRP functions as an anchor to sequester and inhibit GK in the hepatocyte nucleus, where it is protected from degradation. This ensures that glucose phosphorylation is minimal when the liver is in the fasting, glucose-producing phase. This also enables the hepatocytes to rapidly mobilize GK into the cytoplasm to phosphorylate and store or metabolize glucose after the ingestion of dietary glucose. In GKRP-mutant mice, the disruption of this regulation and the subsequent decrease in GK activity leads to altered glucose metabolism and impaired glycemic control.