Laser spot welding of laser textured steel to aluminium

Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel

Total Cross Section, Inelasticity and Multiplicity Distributions in Proton -- Proton Collisions

Multiparticle production in high energy proton -- proton collisions has been analysed in the frame of Strongly Correlated Quark Model (SCQM) of the hadron structure elaborated by the author. It is shown that inelasticity decreases at high energies and this effect together with the total cross section growth and the increasing with collision energy the masses of intermediate clusters result in the violation of KNO -- scaling.Comment: 21 pages, 11 figures, submitted to Yad. Fisik

The effects of nonextensive statistics on fluctuations investigated in event-by-event analysis of data

We investigate the effect of nonextensive statistics as applied to the chemical fluctuations in high-energy nuclear collisions discussed recently using the event-by-event analysis of data. It turns out that very minuite nonextensitivity changes drastically the expected experimental output for the fluctuation measure. This results is in agreement with similar studies of nonextensity performed recently for the transverse momentum fluctuations in the same reactions.Comment: Revised version, to be published in J. Phys. G (2000

Electron stimulated hydroxylation of a metal supported silicate film

Water adsorption on a double-layer silicate film was studied by using infrared reflection–absorption spectroscopy, thermal desorption spectroscopy and scanning tunneling microscopy. Under vacuum conditions, small amounts of silanols (Si–OH) could only be formed upon deposition of an ice-like (amorphous solid water, ASW) film and subsequent heating to room temperature. Silanol coverage is considerably enhanced by low-energy electron irradiation of an ASW pre-covered silicate film. The degree of hydroxylation can be tuned by the irradiation parameters (beam energy, exposure) and the ASW film thickness. The results are consistent with a generally accepted picture that hydroxylation occurs through hydrolysis of siloxane (Si–O–Si) bonds in the silica network. Calculations using density functional theory show that this may happen on Si–O–Si bonds, which are either parallel (i.e., in the topmost silicate layer) or vertical to the film surface (i.e., connecting two silicate layers). In the latter case, the mechanism may additionally involve the reaction with a metal support underneath. The observed vibrational spectra are dominated by terminal silanol groups (ν(OD) band at 2763 cm−1) formed by hydrolysis of vertical Si–O–Si linkages. Film dehydroxylation fully occurs only upon heating to very high temperatures (∼1200 K) and is accompanied by substantial film restructuring, and even film dewetting upon cycling hydroxylation/dehydroxylation treatment

High-accuracy numerical models of Brownian thermal noise in thin mirror coatings

Brownian coating thermal noise in detector test masses is limiting the sensitivity of current gravitational-wave detectors on Earth. Therefore, accurate numerical models can inform the ongoing effort to minimize Brownian coating thermal noise in current and future gravitational-wave detectors. Such numerical models typically require significant computational resources and time, and often involve closed-source commercial codes. In contrast, open-source codes give complete visibility and control of the simulated physics and enable direct assessment of the numerical accuracy. In this article, we use the open-source SpECTRE numerical-relativity code and adopt a novel discontinuous Galerkin numerical method to model Brownian coating thermal noise. We demonstrate that SpECTRE achieves significantly higher accuracy than a previous approach at a fraction of the computational cost. Furthermore, we numerically model Brownian coating thermal noise in multiple sub-wavelength crystalline coating layers for the first time. Our new numerical method has the potential to enable fast exploration of realistic mirror configurations, and hence to guide the search for optimal mirror geometries, beam shapes and coating materials for gravitational-wave detectors

Specific oligomerization of the 5-HT1A receptor in the plasma membrane

In the present study we analyze the oligomerization of the 5-HT1A receptor within living cells at the sub-cellular level. Using a 2-excitation Förster Resonance Energy Transfer (FRET) method combined with spectral microscopy we are able to estimate the efficiency of energy transfer based on donor quenching as well as acceptor sensitization between CFP-and YFP-tagged 5-HT1A receptors at the plasma membrane. Through the analysis of the level of apparent FRET efficiency over the various relative amounts of donor and acceptor, as well as over a range of total surface expressions of the receptor, we verify the specific interaction of these receptors. Furthermore we study the role of acylation in this interaction through measurements of a palmitoylation-deficient 5-HT1A receptor mutant. Palmitoylation increases the tendency of a receptor to localize in lipid rich microdomains of the plasma membrane. This increases the effective surface density of the receptor and provides for a higher level of stochastic interaction

Novel links between ciliopathies and FGF-related craniofacial syndromes

K Liu1*, JT Tabler1, HL Szabo-Rogers1, A Mesbahi1, C Healy1, W Barrell1, B Wlodarczyk2, Author Affiliations 1 King's College London, UK 2 University of Texas Southwestern, USA 3 University of Texas at Austin, USAOral Presentation : Recent studies suggest that planar cell polarity (PCP) genes coordinate cell polarity, ciliogenesis and signalling during mammalian development. FUZ is a PCP gene implicated in human congenital anomalies, including neural tube defects and orofacial clefting. Our analysis of fuzzy mutant mice reveals ciliogenesis defects in craniofacial tissues as well as a suite of phenotypes reminiscent of FGF-related craniofacial disorders. Mutants have coronal synostosis, shortened facial extensions, low-set ears and a high-arched palate. To our surprise, we found that the facial defects are due to increased neural crest migration into the first branchial arch (BA1), resulting in maxillary hyperplasia. Furthermore, the neural crest cells migrate in a disorganized fashion, deeper than normal and with fewer cell-cell contacts. This ectopic migration correlates with a dramatic increase in FGF signaling, first in the mid-hindbrain boundary, and then in the BA1 epithelia. The increased tissue causes a medial positional shift in the palatal primordia that manifests as a high-arched palate with pseudo-cleft. Genetic loss of fgf8 rescues the maxillary hyperplasia. Taken together, our data suggest a novel interplay between ciliogenesis, FGF signalling and migration of neural crest which may underlie congenital craniofacial dysmorphologies.Molecular [email protected]

Antideuteron and deuteron production in mid-central Pb+Pb collisions at 158AA GeV

Production of deuterons and antideuterons was studied by the NA49 experiment in the 23.5% most central Pb+Pb collisions at the top SPS energy of $\sqrt{s_{NN}}$=17.3 GeV. Invariant yields for $\bar{d}$ and $d$ were measured as a function of centrality in the center-of-mass rapidity range $-1.2<y<-0.6$. Results for $\bar{d}(d)$ together with previously published $\bar{p}(p)$ measurements are discussed in the context of the coalescence model. The coalescence parameters $B_2$ were deduced as a function of transverse momentum $p_t$ and collision centrality.Comment: 9 figure