Spinorial Field and Lyra Geometry

The Dirac field is studied in a Lyra space-time background by means of the classical Schwinger Variational Principle. We obtain the equations of motion, establish the conservation laws, and get a scale relation relating the energy-momentum and spin tensors. Such scale relation is an intrinsic property for matter fields in Lyra background.Comment: 10 pages. Some misprints correcte

Accommodation of lattice mismatch in Ge_(x)Si_(1−x)/Si superlattices

We present evidence that the critical thickness for the appearance of misfit defects in a given material and heteroepitaxial structure is not simply a function of lattice mismatch. We report substantial differences in the relaxation of mismatch stress in Ge_(0.5)Si_(0.5)/Si superlattices grown at different temperatures on (100) Si substrates. Samples have been analyzed by x‐ray diffraction, channeled Rutherford backscattering, and transmission electron microscopy. While a superlattice grown at 365 °C demonstrates a high degree of elastic strain, with a dislocation density <10^5 cm^(−2) , structures grown at higher temperatures show increasing numbers of structural defects, with densities reaching 2×10^(10) cm^(−2) at a growth temperature of 530 °C. Our results suggest that it is possible to freeze a lattice‐mismatched structure in a highly strained metastable state. Thus it is not surprising that experimentally observed critical thicknesses are rarely in agreement with those predicted by equilibrium theories

Concentration-independent spontaneously forming biomimetric vesicles

In this Letter we present small-angle neutron scattering data from a biomimetic system composed of the phospholipids dimyristoyl and dihexanoyl phosphorylcholine (DMPC and DHPC, respectively). Doping DMPC-DHPC multilamellar vesicles with either the negatively charged lipid dimyristoyl phosphorylglycerol (DMPG, net charge -1) or the divalent cation, calcium (Ca2+), leads to the spontaneous formation of energetically stabilized monodisperse unilamellar vesicles whose radii are concentration independent and in contrast with previous experimental observations

High Temperature Macroscopic Entanglement

In this paper I intend to show that macroscopic entanglement is possible at high temperatures. I analyze multipartite entanglement produced by the $\eta$ pairing mechanism which features strongly in the fermionic lattice models of high $T_c$ superconductivity. This problem is shown to be equivalent to calculating multipartite entanglement in totally symmetric states of qubits. I demonstrate that we can conclusively calculate the relative entropy of entanglement within any subset of qubits in an overall symmetric state. Three main results then follow. First, I show that the condition for superconductivity, namely the existence of the off diagonal long range order (ODLRO), is not dependent on two-site entanglement, but on just classical correlations as the sites become more and more distant. Secondly, the entanglement that does survive in the thermodynamical limit is the entanglement of the total lattice and, at half filling, it scales with the log of the number of sites. It is this entanglement that will exist at temperatures below the superconducting critical temperature, which can currently be as high as 160 Kelvin. Thirdly, I prove that a complete mixture of symmetric states does not contain any entanglement in the macroscopic limit. On the other hand, the same mixture of symmetric states possesses the same two qubit entanglement features as the pure states involved, in the sense that the mixing does not destroy entanglement for finite number of qubits, albeit it does decrease it. Maximal mixing of symmetric states also does not destroy ODLRO and classical correlations. I discuss various other inequalities between different entanglements as well as generalizations to the subsystems of any dimensionality (i.e. higher than spin half).Comment: 14 pages, no figure

Relationship between the unbinding and main transition temperatures of phospholipid bilayers under pressure

Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, we have studied, as a function of pressure, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC, respectively. We have also reanalyzed data from a number of previously published experiments and have arrived at the following conclusions. (a) The power law behavior describing anomalous swelling is preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. (b) As a function of increasing pressure there is a concomitant decrease in the anomalous swelling of DMPC bilayers. (c) For PC lipids with hydrocarbon chains ≥13 carbons the theoretical unbinding transition temperature T* is coupled to the main gel-to-liquid crystalline transition temperature TM. (d) DLPC is intrinsically different from the other lipids studied in that its T* is not coupled to TM. (e) For DLPC bilayers we predict a hydrostatic pressure (&gt;290MPa) where unbinding may occur

Higher Dimensional Gravity, Propagating Torsion and AdS Gauge Invariance

The most general theory of gravity in d-dimensions which leads to second order field equations for the metric has [(d-1)/2] free parameters. It is shown that requiring the theory to have the maximum possible number of degrees of freedom, fixes these parameters in terms of the gravitational and the cosmological constants. In odd dimensions, the Lagrangian is a Chern-Simons form for the (A)dS or Poincare groups. In even dimensions, the action has a Born-Infeld-like form. Torsion may occur explicitly in the Lagrangian in the parity-odd sector and the torsional pieces respect local (A)dS symmetry for d=4k-1 only. These torsional Lagrangians are related to the Chern-Pontryagin characters for the (A)dS group. The additional coefficients in front of these new terms in the Lagrangian are shown to be quantized.Comment: 10 pages, two columns, no figures, title changed in journal, final version to appear in Class. Quant. Gra

Off-Diagonal Long-Range Order in Bose Liquids: Irrotational Flow and Quantization of Circulation

On the basis of gauge invariance, it is proven in an elementary and straightforward manner, but without invoking any {\it ad hoc} assumption, that the existence of off-diagonal long-range order in one-particle reduced density matrix in Bose liquids implies both the irrotational flow in a simply connected region and the quantization of circulation in a multiply connected region, the two fundamental properties of a Bose superfluid. The origin for both is the phase coherence of condensate wave-functions. Some relevant issues are also addressed.Comment: Revtex, 4 pages, no figure

Symmetries and observables in topological gravity

After a brief review of topological gravity, we present a superspace approach to this theory. This formulation allows us to recover in a natural manner various known results and to gain some insight into the precise relationship between different approaches to topological gravity. Though the main focus of our work is on the vielbein formalism, we also discuss the metric approach and its relationship with the former formalism.Comment: 34 pages; a few explanations added in subsection 2.2.1, published version of pape

Decoding Neural Circuits that Control Compulsive Sucrose Seeking

SummaryThe lateral hypothalamic (LH) projection to the ventral tegmental area (VTA) has been linked to reward processing, but the computations within the LH-VTA loop that give rise to specific aspects of behavior have been difficult to isolate. We show that LH-VTA neurons encode the learned action of seeking a reward, independent of reward availability. In contrast, LH neurons downstream of VTA encode reward-predictive cues and unexpected reward omission. We show that inhibiting the LH-VTA pathway reduces “compulsive” sucrose seeking but not food consumption in hungry mice. We reveal that the LH sends excitatory and inhibitory input onto VTA dopamine (DA) and GABA neurons, and that the GABAergic projection drives feeding-related behavior. Our study overlays information about the type, function, and connectivity of LH neurons and identifies a neural circuit that selectively controls compulsive sugar consumption, without preventing feeding necessary for survival, providing a potential target for therapeutic interventions for compulsive-overeating disorder

The Holst Action by the Spectral Action Principle

We investigate the Holst action for closed Riemannian 4-manifolds with orthogonal connections. For connections whose torsion has zero Cartan type component we show that the Holst action can be recovered from the heat asymptotics for the natural Dirac operator acting on left-handed spinor fields.Comment: We correct a sign mistake in Proposition 2.3. As a consequence the main result (Theorem 3.4) becomes more natura