A six-channel wavelength multiplexer and demultiplexer for single mode systems

We have fabricated and evaluated the first single mode wavelength multiplexer based on a diffraction grating and strip waveguides. The waveguides were employed to minimize the physical spacing between inputs in order to maximize the ratio of channel width to channel separation. The center channel insertion losses for the six channel device were 6.4, 4.9, 6.0, 5.6, 6.8, and 7.8 dB at 1279, 1308, 1338, 1508, 1536, and 1566 nm, respectively. The 1-dB full channel widths averaged 6.0 nm. A matching demultiplexer with multi-mode outputs was also fabricated. The center channel insertion losses were 0.9, 1.1, 1.2, 1.7, 1.8, and 2.1 dB at 1278, 1310, 1337, 1505, 1533, and 1563 nm, respectively. Full 1-dB channel widths ranged from 15 to 11 nm. Out of band rejection exceeded 35 dB.     

Optical observation of growth and melting dynamics of3He-4He mixture crystals

Crystals grown from 2.1% and 9.3% solutions of³ He in⁴He were observed in a cryostat with optical access from two orthogonal directions (above and from the side). Video films of dynamic processes were recorded at temperatures between 0.5K and 1.8K. Facetted melting of crystals (in contrast with rounded melting which is the general case) was observed below 0.75K. This is in accordance with previous experiments which showed a higher³He concentration along the edges of the crystal. We also recorded morphological growth instabilities of the 9.3% b.c.c. crystals. In the temperature region below about 0.9K where the latent heat is negative no dendritic growth was observed, which we interpret as resulting from opposing effects of temperature and concentration gradients.     

Homemade [fabrication technology]

This paper describes the efforts of several universities to investigate technologies and materials that could lead to general-use, compact fabbers machines that rapidly create useful items on demand from computer-generated design specifications. Compact and yet capable fabbers point the way toward a future where the term "online shopping" takes on a whole new meaning. Although many technical hurdles must be cleared before home fabbing can become a reality, it's already possible to see its huge implications for engineers, designers and distributors.     

Synthesis and turnover of polysomal mRNAs in sea urchin embryos

The synthesis and turnover kinetics of polysomal mRNA have been measured in sea urchin embryos. Polysomes were isolated from stages ranging between mesenchyme blastula and late gastrula Strongylocentrotus purpuratus embryos which had been exposed to exogenous 3H-guanosine. The amount of radioactivity incorporated into messenger and ribosomal RNAs was determined separately as a function of time, and the precursor pool specific activity was measured in the same embryos. Synthesis and decay rate constants were extracted from the data by a least-squares procedure. Per embryo, the rate of mRNA synthesis was calculated to be about 0.13 pg min-1, while the rate of rRNA synthesis is about 0.022 pg min-1. The newly synthesized mRNA turns over with a half-time of 5.7 hr. The data support only a single decay rate for the mRNA, but small fractions of mRNA decaying at different rates cannot be excluded. Previous studies have shown that a minor fraction of the mRNA includes the least abundant, most highly diverse set of messages ("complex class" mRNAs). To determine whether mRNAs of the complex class are synthesized and degraded at similar rates, labeled mRNA was measured in hybrids formed in mRNA excess reactions with single copy DNA. These experiments showed that complex class mRNAs represent an approximately proportional amount of the new mRNA symthesis, and turn over at the same average rate as does the bulk of the mRNA. Most of the mRNAs in the embryo polysomes are newly synthesized, rather than maternal. This statement refers both to complex class mRNAs and to prevalent mRNAs. Considering the sequence homology between embryo and oocyte mRNAs shown earlier, these results indicate that many of the same structural genes active during oogenesis are being transcribed in embryos at these stages.     

Quantitative elemental analysis for rhodium and palladium in minerals by time-of-flight resonance ionization mass spectrometry

Results are presented for the trace analysis of Pd and Rh by time-of-flight-resonance ionization mass spectrometry (TOF-RIMS). The spectrometer, developed at the Advanced Mineral Technology Laboratory (Ontario, Canada), is based on a commercial laser-induced mass analyzer with upgrades that include independent laser ablation and ionization sources and pulsed ion optics to minimize noise caused by primary ion formation. The schemes presented for Rh and particularly for Pd detection are simpler than others reported in the literature. The experimental laser fluences were found to be in reasonable agreement with theoretical estimates. The TOF-RIMS measurements were quantified on the basis of calibration curves derived using reference samples covering 3 orders of magnitude in concentration. Minimum detection limits of ~15 parts per billion were found for both metals, with a precision of ~ +/-15%. Samples from sulfide, iron oxide, and silicate minerals were also examined. The results are in excellent agreement with those obtained using dynamics secondary ion mass spectrometry.     

The damping of helicon waves in a tipped magnetic field

The damping of helicon waves in indium was measured under nonlocal conditions with a variable angle between the wave vectorq and the magnetic field. In contrast to the predictions of the free-electron theory, the damping was not a monotonic function of the angle and exhibits considerable structure, which is attributed to minima in the Landau damping for certain orientations of the magnetic field. Minima in the damping are to be expected for such field directions as give rise to cyclotron orbits having a substantial number of electron states with orbital velocities perpendicular toq. In simple situations the critical orientations of the magnetic field may be deduced from a given Fermi surface by a geometrical construction. The construction has been extended to indium, and the tipping angles found are in reasonable agreement with the experiment.Based on a thesis to be submitted to the Senate of the Technion, Israel Institute of Technology, in partial fulfillment of the requirements for D.Sc. degree.     

Growth of CdTel−x Sex by the LEC and bridgman techniques

Large-grain CdTe_l−x Se_x boules with X (nominal) = 0.05, 0.10 and 0.15 have been grown by the liquid-encapsulated Czochralski technique, using B₂O₃ as the encapsulant, and also by a modified Bridgman technique. An argon pressure of 20 atm was used in both techniques. Details of the growth apparatus and procedure are presented. The following characterization methods were used to compare crystals obtained by the two growth techniques: mass spectroscopic analysis, emission spectroscopic analysis, X-ray diffraction analysis, electron probe microanalysis, laser calorimetry at 10.6 μm and infrared transmission as a function of wavelength.