Combining gravity with the forces of the standard model on a cosmological scale

We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the underlying spacetime is a Friedman universe with flat spatial slices and where the matter fields are comprised of the strong interaction, with \SU(3) replaced by a general \SU(n), $n\ge 2$, and the electro-weak interaction. The wave functions are maps from $\R[4n+10]$ to a subspace of the antisymmetric Fock space, and one noteworthy result is that, whenever the electro-weak interaction is involved, the image of an eigenfunction is in general not one dimensional, i.e., in general it makes no sense specifying a fermion and looking for an eigenfunction the range of which is contained in the one dimensional vector space spanned by the fermion.Comment: 53 pages, v6: some typos correcte

Expansion of pinched hypersurfaces of the Euclidean and hyperbolic space by high powers of curvature

We prove convergence results for expanding curvature flows in the Euclidean and hyperbolic space. The flow speeds have the form $F^{-p}$, where $p>1$ and $F$ is a positive, strictly monotone and 1-homogeneous curvature function. In particular this class includes the mean curvature $F=H$. We prove that a certain initial pinching condition is preserved and the properly rescaled hypersurfaces converge smoothly to the unit sphere. We show that an example due to Andrews-McCoy-Zheng can be used to construct strictly convex initial hypersurfaces, for which the inverse mean curvature flow to the power $p>1$ loses convexity, justifying the necessity to impose a certain pinching condition on the initial hypersurface.Comment: 18 pages. We included an example for the loss of convexity and pinching. In the third version we dropped the concavity assumption on F. Comments are welcom

Spin induced gigahertz polarization oscillations in vertical-cavity surface-emitting laser devices

Spin-controlled vertical-cavity surface-emitting lasers (VCSELs) have been intensively studied in recent years because of the low threshold feasibility and the nonlinearity above threshold, which make spin-VCSELs very promising for spintronic devices. Here we investigate the circular polarization dynamics of VCSELs on a picosecond time scale after pulsed optical spin injection at room temperature. A hybrid excitation technique combining continuous-wave (cw) unpolarized electrical excitation slightly above threshold and pulsed polarized optical excitation is applied. The experimental results demonstrate ultrafast circular polarization oscillations with a frequency of about 11 GHz. The oscillations last inside the first undulation of the intensity relaxation oscillations. Via theoretical calculations based on a rate equation model we analyze these oscillations as well as the underlying physical mechanisms

Critical properties of the one-dimensional spin-1/2 antiferromagnetic Heisenberg model in the presence of a uniform field

In the presence of a uniform field the one-dimensional spin-$\frac{1}{2}$ antiferromagnetic Heisenberg model develops zero frequency excitations at field-dependent 'soft mode' momenta. We determine three types of critical quantities, which we extract from the finite-size dependence of the lowest excitation energies, the singularities in the static structure factors and the infrared singularities in the dynamical structure factors at the soft mode momenta. We also compare our results with the predictions of conformal field theory.Comment: 12 pages, REVTEX, 7 figures, submitted to Physical Review

Ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting laser devices

Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications

Acidity changes associated with the keeping quality of apples under various storage conditions

This investigation reports a study of. certain acidity changes occuring in Grimes and Jonathan under various storage conditions. Measurements were made of the total titratable acid, the H-ion concentration and, in some instances, the specific gravity of the juice. Altho total acidity values declined rapidly in the Grimes variety during two weeks of delay at the orchard, its H-ion concentration remained quite uniform. Prolonging the delayed storage period to three weeks, however, resulted in a rather abrupt lowering of the active acidity of the fruit in cold storage. The appearance of soggy breakdown in the stored fruit occurred almost coincidently with a rather marked diminution in the H-ion concentration. This relationship suggests the possibility of an intimate balance between the active acidity and the carbohydrate reserves of the Grimes apple at low temperatures. The H-ion concentration during delayed storage at the orchard, was decidedly more constant in Jonathan. This fact suggests a difference in buffer stability between the two varieties of fruit. The data for the active acidity changes in Jonathan were not of a similar nature during the two storage seasons. Soft scald and Jonathan spot formation also differed for the two years. There appears to be an inverse relationship between the percentage of total acid loss during storage and the susceptibility toward Jonathan spot. A low acid loss during storage usually produced a high percentage of spotted tissue. The total acidity decreased gradually during cold storage in both Grimes and Jonathan. Decrease was more rapid at the higher temperatures. Total acidity decreased more in Grimes during delayed storage at the orchard than thruout the entire cold storage period. The delayed fruit was stored with considerably less total acid than that receiving no such treatment. During storage two conditions appear to influence the total amount of acid lost: (1) The initial acid content when stored, and (2) the storage temperature. Delayed storage lots with low initial acidity lose their total acid in smaller quantities at 30° and 32°F. than similar lots at 34° and 36°F. The amount of acid loss, then, appears to be regulated largely by a certain minimum temperature level, below which the loss will be relatively little regardless of acid content, above which the loss will be considerably higher even tho the acid content is relatively low at the beginning of the storage period. The amount of breakdown tends to occur in an inverse proportion to the losses in total acidity during cold storage. A large amount of soggy breakdown is usually accompanied by a smaller amount of acid loss, and, conversely, a low amount of breakdown is associated with a higher acid loss. In order to avoid soggy breakdown, it follows, then, that the rate of acid loss must be fairly constant. This may be accomplished by storing the fruit before the acid content becomes low (directly after picking), or by storing at a temperature sufficiently high to permit acid losses to continue at a more favorable and a more rapid rate. Altho acid changes appear to be rather definitely associated with breakdown and Jonathan spot susceptibility, other physiological changes occur which may influence these storage disorders. A decided increase in the specific gravity of the juice from Grimes, during delayed storage at the orchard, indicates definite changes in the metabolism of the fruit. Apples delayed for one week showed similar increases in this constant thruout the cold storage period. Little or no increase in specific gravity, however, occurred in the stored fruit which had been delayed at the orchard for two or three weeks. The juice of Jonathan maintained a very uniform constant, irrespective of the delayed storage at the orchard or treatment at the lower temperatures. This different response toward specific gravity and acidity changes in the two varieties may aid in the explanation of the differences in the storage capacity of Grimes and Jonathan. It would appear that the storage capacity of some varieties of apples could be forecast by changes appearing in the specific gravity of their juices

Birefringence controlled room-temperature picosecond spin dynamics close to the threshold of vertical-cavity surface-emitting laser devices

We analyze the spin-induced circular polarization dynamics at the threshold of vertical-cavity surface-emitting lasers at room-temperature using a hybrid excitation combining electrically pumping without spin preference and spin-polarized optical injection. After a short pulse of spin-polarized excitation, fast oscillations of the circular polarization degree (CPD) are observed within the relaxation oscillations. A theoretical investigation of this behavior on the basis of a rate equation model shows that these fast oscillations of CPD could be suppressed by means of a reduction of the birefringence of the laser cavity

Blood flow boosts BMP signaling to keep vessels in shape

Bone morphogenic proteins (BMPs) and blood flow regulate vascular remodeling and homeostasis. In this issue, Baeyens et al. (2016. J. Cell Biol http://dx.doi.org/10.1083/jcb.201603106) show that blood flow sensitizes endothelial cells to BMP9 signaling by triggering Alk1/ENG complexing to suppress cell proliferation and to recruit mural cells, thereby establishing endothelial quiescence

“ENDOTROPHIC” SPORULATION

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72259/1/j.1749-6632.1963.tb13674.x.pd