Spin-Spin Interaction In Matrix Theory

We calculate the spin dependent static force between two D0-branes in Matrix theory. Supersymmetry relates velocity dependent potentials to spin dependent potentials. The well known v^4/r^7 term is related to a theta^8/r^11 term, where theta is the relative spin of the D0-branes. We calculate this term, confirming that it is the lowest order contribution to the static potential, and find its structure consistent with supergravity.Comment: 15 pages, LaTeX, uses feynmf.sty for diagrams. Reference added and some labels on the diagrams restore

Uncharged tRNA Activates GCN2 by Displacing the Protein Kinase Moiety from a Bipartite tRNA-Binding Domain

Protein kinase GCN2 regulates translation in amino acid–starved cells by phosphorylating eIF2. GCN2 contains a regulatory domain related to histidyl-tRNA synthetase (HisRS) postulated to bind multiple deacylated tRNAs as a general sensor of starvation. In accordance with this model, GCN2 bound several deacylated tRNAs with similar affinities, and aminoacylation of tRNAPhe weakened its interaction with GCN2. Unexpectedly, the C-terminal ribosome binding segment of GCN2 (C-term) was required in addition to the HisRS domain for strong tRNA binding. A combined HisRS+C-term segment bound to the isolated protein kinase (PK) domain in vitro, and tRNA impeded this interaction. An activating mutation (GCN2c-E803V) that weakens PK–C-term association greatly enhanced tRNA binding by GCN2. These results provide strong evidence that tRNA stimulates the GCN2 kinase moiety by preventing an inhibitory interaction with the bipartite tRNA binding domain

Una aproximación jerárquica a la cartografía del espesor del suelo en ambientes semiáridos

[Resumen] Se explora la producción de mapas de profundidad del suelo construyendo y modelizando un sistema de relaciones espaciales entre muestras georeferenciadas y variables topográficas derivadas de un Modelo Digital de Elevación a 30 m de resolución. El muestreo sigue una estratificación jerarquizada cuya representatividad se mantiene, de modo que el modelo producido es aplicable al total del territorio. El trabajo se ha realizado en dos pequeñas cuencas (20 km2) dentro del valle del Guadalentín (3300 km2), un territorio semiárido del sureste peninsular. La precisión de los mapas resultantes está en el intervalo 61-81%para pizarras, 40-55% para filitas y 72-78% para calizas. La baja precisión obtenida para las filitas parece relacionada con la imposibilidad de detectar sus facetas topograficas a la resolución de trabajo..[Abstract] We explored a method to produce soil depth maps that is based on the spatial modelling of a system of relationships between georeferenced field samples and topographic variables derived from a Digital Elevation Model at the 30 m resolution. The sampling design follows a hierarchical stratification to ensure representativeness, so that the model relationships may be applied to the entire territory. The work has been carried out in two small basins of 20 km2 within the basin of the Guadalentin, a 3300 km2 territory in SE Spain. The accuracy of the resulting maps ranges from 61 to 81%in shales, 40-55% in phyllite, and 72-78% in limestones. The low results obtained for phyllites seem to be related to undetected topographic features at the work resolution

Stability conditions for the solutions of the Half-Projected Hartree-Fock scheme. The lithium-hydride ground state

4 págs.; 1 fig.; 2 tabs.The stability conditions for the solutions of a two-unrestricted-determinant function (the half-projected Hartree-Fock function) are deduced from the necessary requirements for the minimization of the energy functional. The theory is applied to the case of the LiH ground state, in order to investigate the various solutions encountered in the variational problem. It is found that the two lowest solutions are local minima. The number of these solutions is estimated and their significance discussed as a function of the nuclear separation. © 1977 The American Physical Society.Peer Reviewe

Quantification of the morphological characteristics of hESC colonies

The maintenance of the undifferentiated state in human embryonic stem cells (hESCs) is critical for further application in regenerative medicine, drug testing and studies of fundamental biology. Currently, the selection of the best quality cells and colonies for propagation is typically performed by eye, in terms of the displayed morphological features, such as prominent/abundant nucleoli and a colony with a tightly packed appearance and a well-defined edge. Using image analysis and computational tools, we precisely quantify these properties using phase-contrast images of hESC colonies of different sizes (0.1–1.1 mm2) during days 2, 3 and 4 after plating. Our analyses reveal noticeable differences in their structure influenced directly by the colony area A. Large colonies (A > 0.6 mm2) have cells with smaller nuclei and a short intercellular distance when compared with small colonies (A  0.6 mm2) due to the proliferation of the cells in the bulk. This increases the colony density and the number of nearest neighbours. We also detect the self-organisation of cells in the colonies where newly divided (smallest) cells cluster together in patches, separated from larger cells at the final stages of the cell cycle. This might influence directly cell-to-cell interactions and the community effects within the colonies since the segregation induced by size differences allows the interchange of neighbours as the cells proliferate and the colony grows. Our findings are relevant to efforts to determine the quality of hESC colonies and establish colony characteristics database

Using the Sound Card as a Timer

Experiments in mechanics can often be timed by the sounds they produce. In such cases, digital audio recordings provide a simple way of measuring time intervals with an accuracy comparable to that of photogate timers. We illustrate this with an experiment in the physics of sports: to measure the speed of a hard-kicked soccer ball.Comment: 3 pages, 4 figures, Late

Quantification of the morphological characteristics of hESC colonies

The maintenance of the pluripotent state in human embryonic stem cells (hESCs) is critical for further application in regenerative medicine, drug testing and studies of fundamental biology. Currently, the selection of the best quality cells and colonies for propagation is typically performed by eye, in terms of the displayed morphological features, such as prominent/abundant nucleoli and a colony with a tightly packed appearance and a well-defined edge. Using image analysis and computational tools, we precisely quantify these properties using phase-contrast images of hESC colonies of different sizes (0.1 -- 1.1$\, \text{mm}^2$) during days 2, 3 and 4 after plating. Our analyses reveal noticeable differences in their structure influenced directly by the colony area $A$. Large colonies ($A > 0.6 \, \text{mm}^2$) have cells with smaller nuclei and a short intercellular distance when compared with small colonies ($A < 0.2 \, \text{mm}^2$). The gaps between the cells, which are present in small and medium sized colonies with $A \le 0.6 \, \text{mm}^2$, disappear in large colonies ($A > 0.6 \, \text{mm}^2$) due to the proliferation of the cells in the bulk. This increases the colony density and the number of nearest neighbours. We also detect the self-organisation of cells in the colonies where newly divided (smallest) cells cluster together in patches, separated from larger cells at the final stages of the cell cycle. This might influence directly cell-to-cell interactions and the community effects within the colonies since the segregation induced by size differences allows the interchange of neighbours as the cells proliferate and the colony grows. Our findings are relevant to efforts to determine the quality of hESC colonies and establish colony characteristics database

Cerebral Air Embolism from Angioinvasive Cavitary Aspergillosis

Background. Nontraumatic cerebral air embolism cases are rare. We report a case of an air embolism resulting in cerebral infarction related to angioinvasive cavitary aspergillosis. To our knowledge, there have been no previous reports associating these two conditions together. Case Presentation. A 32-year-old female was admitted for treatment of acute lymphoblastic leukemia (ALL). Her hospital course was complicated by pulmonary aspergillosis. On hospital day 55, she acutely developed severe global aphasia with right hemiplegia. A CT and CT-angiogram of her head and neck were obtained demonstrating intravascular air emboli within the left middle cerebral artery (MCA) branches. She was emergently taken for hyperbaric oxygen therapy (HBOT). Evaluation for origin of the air embolus revealed an air focus along the left lower pulmonary vein. Over the course of 48 hours, her symptoms significantly improved. Conclusion. This unique case details an immunocompromised patient with pulmonary aspergillosis cavitary lesions that invaded into a pulmonary vein and caused a cerebral air embolism. With cerebral air embolisms, the acute treatment option differs from the typical ischemic stroke pathway and the provider should consider emergent HBOT. This case highlights the importance of considering atypical causes of acute ischemic stroke