Possible Tests of Curvature Effects in Weak Gravitational Fields

The possibility of performing in proximity of the Earth experiments to test the predictions of general relativity for the trajectories of particles and photons in weak gravitational fields is studied. Three experiments are analyzed, all based on optical detection methods. The first experiment would allow to detect the tidal acceleration using a freely-falling Michelson interferometer. In a second experiment, based on laser-ranging methods, the relativistic correction to the classical gravity acceleration could be detected. Finally, the possibility of detecting light deflection induced by space curvature in an optical cavity with high-reflectivity mirrors is discussed.     

Investigation of the B2Σ and test of the A2II interaction potential for Na(32P)-Ar from high-resolution differential scattering measurements

We have measured differential cross sections for scattering of laser-excited Na(3²P_{$\text{3}\text{2}$}) by Ar(¹S₀) at thermal collision energies with high angular resolution (0.1°). In the investigated range of scattering angles (1°–15°) the cross sections contain contributions from scattering along the excited state B²Σ potential (rainbow scattering) and the A²II potential (supernumerary rainbows). By performing fit calculations in which the spectroscopically determined A²II potential was adopted we were able to obtain information about the B²Σ potential. With the assumption of a Lennard-Jones (12.6) potential shape we obtain a well depth ?^BΣ = (0.14±0.02)×10^?3 au and an equilibrium distance r_m^BΣ = 10.4±1.0 au. This work presents the first experimental determination of the B²Σ potential well parameters.     

Spectroscopy of the 689 nm intercombination line of strontium using an extended-cavity InGaP/InGaAIP diode laser

A visible diode laser emitting at 690 nm at room temperature has been frequency-stabilized using a simple scheme based on optical feedback from a diffraction grating. The possibilities offered by these lasers for high-resolution spectroscopy are demonstrated by recording the sub-Doppler signal of the 689 nm intercombination line of strontium and resolving the hyperfine structure of the close P63 R70 (8, 4) transitions of iodine.     

Tunable frequency-controlled laser source in the near ultraviolet based on doubling of a semiconductor diode laser

Continuously tunable ultraviolet laser radiation at 397 nm was generated by doubling the output of a semiconductor diode laser. The fundamental radiation was provided by a 150 mW AlGaAs laser diode injected by a low-power AlGaAs laser diode which was frequency stabilized by optical feedback using a new scheme of a miniature external cavity. Second-harmonic generation was produced in a lithium-triborate crystal placed in a compact enhancement cavity. The fundamental radiation was used for sub-Doppler spectroscopy of the Ar I 4s ³ P ⁰ ₀–4p ¹ P ₁ transition at 795 nm; the second-harmonic radiation was used for spectroscopy of the Ca II 4² S _1/2–4² P _1/2 transition at 397 nm.     

Natural bounded concentrators

We give the first known direct construction for linear families of bounded concentrators. The construction is explicit and the results are simple natural bounded concentrators. Let be the field withq elements,g(x)∈F _q [x] of degree greater than or equal to 2, and . LetI _nputs=H/A,O _utputs=H/B, and draw an edge betweenaA andbB iffaA∩bB≠ϕ. We prove that for everyq≥5 this graph is an concentrator. Part of this research was done while the author was at the department of Computer Science, The University of British Columbia, Vancouver, B.C., Canada.     

The mass spectra of organic compounds. 7th Communication. 4,4-Dimethyl-1-pentene

Loss of CH, CH₄, C₂H₄, C₃H, C₃H₆ and C₃H₇ from the molecular ions of a number of ¹³C-labeled analogs of 4,4-dimethyl-1-pentene was studied both in normal (source) 70-eV electron impact (EI) spectra dn in metastable spectra. For loss of CH in the source, 96% of the methyl comes frm positions of 5, 5′ and 5″, while the remainder comes from position 1. In the metastable spectra, loss of C-1 (16%) and C-3 (9%) is increasing in importance. The loss of ethylene is a particular case: either C-1 or C-3 are lost with any other C-atom from positions 2,5,5′, and 5″ (8 × 10%) in the metastable spectra, the probability for simultaneous loss of C-1 and C-3 being 6%. If C-1 seems to these two positions become completely equivalent in the metastable time range. The T-values (kinetic energy release) for the different positions show small, but statisticaly different values and a small isotope effect. Loss of C₃H₅ (allylic cleavage) is 100% C-1, C-2 and C-3, i.e., no evidence for skeletal rearrangement is seen. This is also true for loss of C₃C₆ (McLafferty rearrangement) within the source, but in metastable decay the other positions gain in importance. The neutral fragment C₃H appears to be the the result of consecutive loss of CH and C₃H₄, rather than a one-step loss of propyl radical or the inverse reactions sequence. No metastable reaction can be seen for this reaction. Decomposition of labeled C₆H and C₅H secondary ions occurs in an essentially random fashion.     

Anomalous dissociative behavior of the major glycosylated component of the cellulosome of clostridium thermocellum

The cellulosome of Clostridium thermocellum is a highly cohesive multienzyme complex that is capable of completely solubilizing insoluble cellulose. One of the major cellulosomal components, the glycosylated S1 subunit, is believed to play an important structural role and normally migrates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an Mr of 210,000. It is shown here that by simply altering the conditions (pH or ionic strength) of the environment prior to electrophoresis, a different migratory profile for S1 emerges, yielding a collection of bands, all of which migrate faster than the parent band. The original electrophoretic behavior of S1 can be reproduced on restoration of the original pH and ionic strength. These results may bear important significance for the physiological role of the S1 subunit in facilitating the observed synergistic action of the other (cellulolytic) components of the cellulosome.     

Magnetic correlations in three-dimensional ising spin glasses

By a recursive method numerically exact free energies are calculated forL×L×M Ising lattices with random bonds andL=4, 4M10, applying free boundaries in the direction where the lattice is less small and otherwise periodic boundary conditions. Both for the±J model and the gaussian model the specific heat is in fair agreement with Monte Carlo results obtained for much larger lattices. However, the correlation function [S ₀ S _{R T} ² ]_av is found to decay exponentially with distanceR [for 1R9] at temperatures far below the apparent freezing temperatures of the Monte Carlo simulations, implying that there is no nonzero Edwards-Anderson order parameter in equilibrium. This behavior is qualitatively different from Mattis spin glasses (or Ising ferromagnets) where even smaller lattices show pronounced magnetic order at low temperatures. As the Monte Carlo results give evidence for a nonzero Edwards-Anderson order parameter (for not too long observation times), which is fairly independent of lattice size down to sizes of 4³, we suggest that Edwards-Anderson ordering is a nonequilibrium phenomenon visible only in studying dynamic properties.     

Changes in cellulose structure during dissolution in LiCl:N,N-dimethylacetamide and in the alkaline iron tartrate system EWNN

The influence of different solvents on the morphology of cellulose during the dissolution process was studied. Spruce sulfite pulp, cotton linters and hydrolysed cotton linters were treated for a short time with lithium chloride: N,N-dimethylacetamide (LiCl:DMAc) and an alkaline solution of iron sodium tartrate (EWNN), respectively. The changes occurring at the fibre surfaces and within the cell walls were observed by scanning as well as by transmission electron microscopy. The cellulose fibres show significant differences in the dissolution behaviour when comparing the reaction of the two solvents. Using LiCl:DMAc, the cotton linters fibres become lamellar separated and within the spruce sulfite pulp fibres solvent channels appear in the first step with the fibrils becoming separated. In contrast, EWNN has a swelling effect on the surface of the cellulose fibres. Both solvent systems predominantly affect the ends of the fibres and places where the wall structure has been damaged.