Infinite-dimensional representations of the rotation group and Dirac's monopole problem

Within the context of infinite-dimensional representations of the rotation group the Dirac monopole problem is studied in details. Irreducible infinite-dimensional representations, being realized in the indefinite metric Hilbert space, are given by linear unbounded operators in infinite-dimensional topological spaces, supplied with a weak topology and associated weak convergence. We argue that an arbitrary magnetic charge is allowed, and the Dirac quantization condition can be replaced by a generalized quantization rule yielding a new quantum number, the so-called topological spin, which is related to the weight of the Dirac string.Comment: JHEP style. Extended version of hep-th/0403146. Revised version, title and some notations are changed. References and Appendix B are adde

Gold(I) Carbenoids: On-Demand Access to Gold(I) Carbenes in Solution

Chloromethylgold(I) complexes of phosphine, phosphite, and N-heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors. Activation of these gold(I) carbenoids with a variety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene, olefin cyclopropanation, and Buchner ring expansion of benzene

Morphologic and morphometric study of the musculus obliquus dorsalis of the dog

In the present investigation, the dorsal oblique muscle of the right ocular globe was removed from six adult dogs weighing 40-50 kg and analyzed by light microscopy. Muscle samples were taken from the central portion of the muscle belly, subsequently ultrafrozen, cut and stained with m-ATPase at pH 4.6. Fibers were classified as type I or type II according to their reaction to the m-ATPase and detailed morphologic and morphometric studies were made. The muscles showed two clearly distinct layers, a central layer and a peripheral layer, mainly composed of type II fibers. The fibers in the central layer were larger in size than those in the peripheral layer. The peculiar stratigraphy of the dorsal oblique muscle should be taken into account when performing analyses of this muscle and investigating the significance of the fiber types it contains.En el presente trabajo se han extraído, de los globos oculares derechos, de seis perros adultos de 40-50 kilogramos de peso, los músculos oblicuos dorsales y analizados con microscopia de luz. Las muestras musculares para su análisis se tomaron de la porción central del vientre muscular y fueron ultracongeladas, cortadas y teñidas por la técnica de m-ATPasa a pH 4,6. Las fibras se clasificaron en tipo I y tipo II en virtud a su reacción frente a la m-ATPasa, realizándose un detallado estudio morfológico y morfométrico. Los músculos presentaron dos estratos netamente diferenciados, uno central y otro periférico, compuestos mayoritariamente por fibras tipo II. Las fibras del estrato central presentaron un mayor tamaño que las correspondientes del estrato periférico. La peculiar estratigrafía del músculo oblicuo dorsal debería tenerse en consideración al analizar este músculo e investigar el significado de los tipos fibrilares que contien

Genomic architecture of parallel ecological divergence : beyond a single environmental contrast

The study of parallel ecological divergence provides important clues to the operation of natural selection. Parallel divergence often occurs in heterogeneous environments with different kinds of environmental gradients in different locations, but the genomic basis underlying this process is unknown. We investigated the genomics of rapid parallel adaptation in the marine snail Littorina saxatilis in response to two independent environmental axes (crab-predation versus wave-action and low-shore versus high-shore). Using pooled whole-genome resequencing, we show that sharing of genomic regions of high differentiation between environments is generally low but increases at smaller spatial scales. We identify different shared genomic regions of divergence for each environmental axis and show that most of these regions overlap with candidate chromosomal inversions. Several inversion regions are divergent and polymorphic across many localities. We argue that chromosomal inversions could store shared variation that fuels rapid parallel adaptation to heterogeneous environments, possibly as balanced polymorphism shared by adaptive gene flow

Mechanical Properties of Chaperone BiP, the Master Regulator of the Endoplasmic Reticulum

Immunoglobulin heavy-chain-binding protein (BiP protein) is a 75-kDa Hsp70 monomeric ATPase motor that plays broad and crucial roles maintaining proteostasis inside the cell. Its malfunction has been related with the appearance of many and important health problems such as neurodegenerative diseases, cancer, and heart diseases, among others. In particular, it is involved in many endoplasmic reticulum (ER) processes and functions, such as protein synthesis, folding, and assembly, and also it works in the posttranslational mechanism of protein translocation. However, it is unknown what kind of molecular motor BiP works like, since the mechanochemical mechanism that BiP utilizes to perform its work during posttranslational translocation across the ER is not fully understood. One novel approach to study both structural and catalytic properties of BiP considers that the viscoelastic regime behavior of the enzymes (considering them as a spring) and their mechanical properties are correlated with catalysis and ligand binding. Structurally, BiP is formed by two domains, and to establish a correlation between BiP structure and catalysis and how its conformational and viscoelastic changes are coupled to ligand binding, catalysis, and allosterism (information transmitted between the domains), optical tweezers and nano-rheology techniques have been essential in this regard

Counting matrices over finite fields with support on skew Young diagrams and complements of Rothe diagrams

We consider the problem of finding the number of matrices over a finite field with a certain rank and with support that avoids a subset of the entries. These matrices are a q-analogue of permutations with restricted positions (i.e., rook placements). For general sets of entries these numbers of matrices are not polynomials in q (Stembridge 98); however, when the set of entries is a Young diagram, the numbers, up to a power of q-1, are polynomials with nonnegative coefficients (Haglund 98). In this paper, we give a number of conditions under which these numbers are polynomials in q, or even polynomials with nonnegative integer coefficients. We extend Haglund's result to complements of skew Young diagrams, and we apply this result to the case when the set of entries is the Rothe diagram of a permutation. In particular, we give a necessary and sufficient condition on the permutation for its Rothe diagram to be the complement of a skew Young diagram up to rearrangement of rows and columns. We end by giving conjectures connecting invertible matrices whose support avoids a Rothe diagram and Poincar\'e polynomials of the strong Bruhat order.Comment: 24 pages, 9 figures, 1 tabl

Reversible collapse of insoluble monolayers

II Encuentro sobre nanociencia y nanotecnología de investigadores y tecnólogos de la Universidad de Córdoba. NANOUC

Colapso reversible de monocapas insolubles. Influencia de la línea de tensión de los dominios

II Encuentro sobre nanociencia y nanotecnología de investigadores y tecnólogos de la Universidad de Córdoba. NANOUC

Determination of protein-protein interactions at the single-molecule level using optical tweezers

Biomolecular interactions are at the base of all physical processes within living organisms; the study of these interactions has led to the development of a plethora of different methods. Among these, single-molecule (in singulo) experiments have become relevant in recent years because these studies can give insight into mechanisms and interactions that are hidden for ensemble-based (in multiplo) methods. The focus of this review is on optical tweezer (OT) experiments, which can be used to apply and measure mechanical forces in molecular systems. OTs are based on optical trapping, where a laser is used to exert a force on a dielectric bead; and optically trap the bead at a controllable position in all three dimensions. Different experimental approaches have been developed to study protein-protein interactions using OTs, such as: (1) refolding and unfolding in trans interaction where one protein is tethered between the beads and the other protein is in the solution; (2) constant force in cis interaction where each protein is bound to a bead, and the tension is suddenly increased. The interaction may break after some time, giving information about the lifetime of the binding at that tension. And (3) force ramp in cis interaction where each protein is attached to a bead and a ramp force is applied until the interaction breaks. With these experiments, parameters such as kinetic constants (koff, kon), affinity values (KD), energy to the transition state ΔG≠, distance to the transition state Δx≠ can be obtained. These parameters characterize the energy landscape of the interaction. Some parameters such as distance to the transition state can only be obtained from force spectroscopy experiments such as those described here

Morphometric study of the nerve fibers of the oculomotor nerve in dog

The intracranial portion of the right oculomotor nerves was extracted from six adult German Shepherd dogs. The nerves were studied using light and electron microscopy. Nerve area was calculated, and myelinated and unmyelinated fibers were analized to determine number, diameter and area. Also in the myelinated fibers the area and diameter of the correspondent axon, and thickness of the myeline sheath were measured. The mean number of fibers was 8543.50±1231.85 for myelinated and 1402.00±241.58 for unmyelinated. The mean fiber diameter was 10.23±0.68 μm for myelinated and 0.43±0.21 μm for unmyelinated. This study demonstrated that the oculomotor nerves in dogs have structural and ultrastructural characteristics that are similar to those from other specie