Galaxy Formation by Galactic Magnetic Fields

Galaxies exhibit a sequence of various morphological types, i.e., the Hubble sequence, and they are basically composed of spheroidal components (elliptical galaxies and bulges in spiral galaxies) and disks. It is known that spheroidal components are found only in relatively massive galaxies with M=10^{10-12} M_sun, and all stellar populations in them are very old, but there is no clear explanation for these facts. Here we present a speculative scenario for the origin of the Hubble sequence, in which magnetic fields ubiquitously seen in galaxies have played a crucial role. We first start from a strange observational fact that magnetic field strengths observed in spiral galaxies sharply concentrate at a few microgauss, for a wide range of galaxy luminosity and types. We then argue that this fact and the observed correlation between star formation activity and magnetic field strength in spiral galaxies suggest that spheroidal galaxies have formed by starbursts induced by strong magnetic fields. Then we show that this idea naturally leads to the formation of spheroidal systems only in massive and high-redshift objects in hierarchically clustering universe, giving a simple explanation for various observations.Comment: 7 pages including 2 figures. Accepted by ApJ Letter

Coherent acoustic vibration of metal nanoshells

Using time-resolved pump-probe spectroscopy we have performed the first investigation of the vibrational modes of gold nanoshells. The fundamental isotropic mode launched by a femtosecond pump pulse manifests itself in a pronounced time-domain modulation of the differential transmission probed at the frequency of nanoshell surface plasmon resonance. The modulation amplitude is significantly stronger and the period is longer than in a gold nanoparticle of the same overall size, in agreement with theoretical calculations. This distinct acoustical signature of nanoshells provides a new and efficient method for identifying these versatile nanostructures and for studying their mechanical and structural properties.Comment: 5 pages, 3 figure

TRIDENT: an infrared camera optimized for the detection of methanated substellar companions around nearby stars

A near-infrared (0.85-2.5 microns) camera in use at the Canada-France-Hawaii Telescope and at the 1.6m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, enabling an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronagraph and features a fast (1 MHz) data acquisition system without reset anomaly, yielding high observing efficiencies on bright stars. The performance of the instrument is described, and it is illustrated by CFHT images of the nearby star Ups And. TRIDENT can detect (3 sigma) a methanated companion with DeltaH=10 at 0.5 arcsec from the star in one hour of observing time. Non-common path aberrations between the three optical paths are the limiting factors preventing further PSF attenuation. Reference star subtraction and instrument rotation improve the detection limit by one order of magnitude.Comment: 8 pages, 6 figures, to appear in SPIE 486

Identification of Materials’ Mechanical parameters

The purpose of this study is to set the numerical bases before approaching the study of the identification of the mechanical parameters of materials’ elastic behavior. Indeed, most part of the mechanical tests do not allow to identify these mechanical parameters, the use of finite elements method calculations to design structures is limited by a poor knowledge of the mechanical properties. It is in this context that arises the inverse analysis problematic [ 1 ] [ 2 ]. For the parameters of the behaviour laws of material ; what information can be obtained from the in situ measures ? Besides what are the numerical techniques needed to obtain a determination of these parameters precisely and systematically. In this work we present a new way of proceeding by proposing an easy useful formulation by a treatment of the inverse problem. The problem so found is a differential system instead of a partial derivative problem. The resolution of the direct problem leads to obtain convincing results. These latters are in agreement with the simulation by a commercial code. This will allow us afterward to approach, without apprehension, the inverse problem. This is achieves through proposing a technique of systematic identification by using the database beforehand definite [3]

Establishing the entatic state in folding metallated Pseudomonas aeruginosa azurin

Understanding how the folding of proteins establishes their functional characteristics at the molecular level challenges both theorists and experimentalists. The simplest test beds for confronting this issue are provided by electron transfer proteins. The environment provided by the folded protein to the cofactor tunes the metal's electron transport capabilities as envisioned in the entatic hypothesis. To see how the entatic state is achieved one must study how the folding landscape affects and in turn is affected by the metal. Here, we develop a coarse-grained functional to explicitly model how the coordination of the metal (which results in a so-called entatic or rack-induced state) modifies the folding of the metallated Pseudomonas aeruginosa azurin. Our free-energy functional-based approach directly yields the proper nonlinear extra-thermodynamic free energy relationships for the kinetics of folding the wild type and several point-mutated variants of the metallated protein. The results agree quite well with corresponding laboratory experiments. Moreover, our modified free-energy functional provides a sufficient level of detail to explicitly model how the geometric entatic state of the metal modifies the dynamic folding nucleus of azurin

Analysis of Vibracores from the New Hampshire Continental Shelf from 1984 and 1988

During this study, the twenty-three vibracores taken in 1984 and 1988 were reexamined, original descriptions verified and significantly expanded, and the cores sampled to provide complete grain size data (i.e. the original sediment grain size analyses were limited). The vibracores were grouped by location with respect to major physiographic features (geoforms) or surficial sediment type including Offshore Marine-Modified Glacial Features (Drumlins and Lodgement Till Deposits), Northern Sand Body, Isles of Shoals, Nearshore Marine-Modified Glacial Features (Eskers and Drumlins), Nearshore Sheet Sand, and Offshore Seafloor Plain. The Northern Sand Body (NSB), located near the Isles of Shoals ~10 km from shore, is relatively large measuring ~3.2km in length and ~1.3km in width, with a maximum relief of ~7m. Earlier studies estimated the NSB may contain as much as 17 million m3 of sand and gravel, but this has not been verified. One of the vibracores taken at the northern end of the NSB has ~3.6m of medium to coarse sand with varying amounts of fine gravel overlying fine sand. Similarly, a vibracore from near the center of the NSB has ~3.1m of slightly granuley medium sand with shell fragments and scattered pebbles overlying fine sands. However, other vibracores taken at the NSB are largely fine to very fine sand of varying thickness. The NSB likely formed from deposits that were originally either a marine glacial delta, a subaqueous delta, or sandy outwash that was heavily modified by marine processes. A vibracore taken on top of an offshore drumlin-like feature located ~24km from shore has ~4.7m of medium to coarse sand overlying fine sand and silty very fine sand to silt deposits. The upper sands likely represent a lag deposit formed by wave action during the last sea-level lowstand. However, it is not known if this lag deposit continues over the surface of the entire drumlin. Except for the NSB, and potentially the offshore drumlin, the other sand and gravel deposits examined are relatively small in aerial extent. However, several of the marine-modified glacial deposits have approximately three to five meters of sand and gravel. For example, a vibracore taken near an esker-like feature had ~5.75m of very coarse sand to gravelly sediments composing the matrix (the largest clasts were not measured due to limited sample size). The eskers were exposed during the last sea-level lowstand and were modified by shallow water waves and nearshore process during the Holocene transgression. The esker was likely eroded, the large gravel left as a lag deposit, and the finer sediment deposited as nearby shoals. The Nearshore Sheet Sand deposits located within a few kilometers of the coast are relatively thin (less than ~2.5m), flat-lying layers of sand and gravel unconformably overlying glacial marine sandy mud which were likely formed from reworked glacial marine sediment during the last transgression, especially wave-modified marine deltas or outwash. In addition, the deposits are likely part of the nearshore sand ramp extending from the beaches in southern NH

Surficial Geology of the Continental Shelf off New Hampshire: Morphologic Features and Surficial Sediment

The continental shelf off New Hampshire (NH) in the Western Gulf of Maine (WGOM) is extremely complex and includes extensive bedrock outcrops, marine-modified glacial deposits, marine-formed shoals, seafloor plains, and associated features that are composed of a range of sediment types from mud to gravel. Furthermore, the physiography and composition of the seafloor frequently changes dramatically over relatively short distances (tens of meters). The complexity of the WGOM seafloor results from the interplay of glaciations, sea-level fluctuations, and marine processes (waves and currents). High-resolution multibeam echosounder (MBES) bathymetry and backscatter surveys, along with ground truth consisting of archived seismic reflection profiles, bottom sediment grain size data, vibracores, and video were used to develop surficial geology maps based on the Coastal and Marine Ecological Classification Standard (CMECS). The surficial geology maps cover ~3,250 km2 and extend from the coast of NH seaward ~50 km to Jeffreys Ledge and depict major geoforms (physiographic features) and seafloor substrate (sediment size) classifications. CMECS provides a sound basis for classifying the texture of the seafloor; however, the geoform classifications need to be broadened for paraglacial environments in future studies. The surficial geology maps presented here are a major refinement of the original maps produced in 2016 (see Ward et al., 2016a). The new maps reflect the results of a major field campaign conducted in 2016-2017 to obtain accurately located sediment samples and seafloor images to complement the original bottom sediment database. The new sites specifically targeted areas where high-resolution MBES bathymetry existed or where surficial features warranted further ground truth for evaluations. This work was designed to enhance the surficial geology mapping efforts and contribute to the development of new approaches for utilizing acoustics to remotely classify seafloor sediments and morphologic features (also supported by the University of New Hampshire Joint Hydrographic Center). The new surficial geology maps presented here depict the exposed bedrock, morphologic features, and sediment distribution on the continental shelf off NH, revealing features of the seafloor in exceptional detail that have not been previously described. An important finding of this study was the extent and importance of marine-modified glacial features on the WGOM continental shelf. Extensive glacial deposits including drumlins, eskers, outwash, and moraines have been eroded and modified by wave and tidal currents as sea level fluctuated over the last 12,000 years. These features are potential sources of sand and gravel for future beach nourishment projects; however, more detailed subbottom seismic surveys and vibracores are needed for verification. Also, these potential resource areas are presently too far from shore and in too great a depth of water to be easily utilized. As the demand for sand and gravel becomes more acute and technologies advance, mineral resources farther offshore and in deeper water will likely become viable

Coarctation of the aorta: pre and postoperative evaluation with MRI and MR angiography; correlation with echocardiography and surgery

Aims: To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation. Materials and methods: 136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA. Results: In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases. Conclusions: MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowin