Mechanism for self-synchronization of femtosecond pulses in atwo-color Ti:sapphire laser

An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model     

Insertional re-activation of a chloramphenicol acetyltransferase misfolding mutant protein

The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding.     

Modeling of Diffusion in Capillary Porous Materials During the Drying Process

This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.     

Low-temperature phase transformation in Li-10 at. % Mg

It is not known whether impaired hematopoiesis noted during human immunodeficiency virus (HIV) infection results from infection of stem/progenitor cells or of cells of the bone marrow microenvironment. Normal adherent primary stromal layers were exposed to HIV to determine which of this mixture of endothelial cells, fibroblasts, and macrophages are susceptible to the virus. Viral p24 in supernatants was noted with monocytotropic HIV-1Ada, HIV-1Ba-L, and HIV-1JR-FL but not with lymphotropic HIV-1LAI nor HIV-1MN strain, and only stromal macrophages expressed the viral antigens. Coculture of the layers with PHA-activated normal lymphocytes failed to rescue lymphotropic virus. No p24 was produced when macrophage-depleted stromal cells were exposed to either HIV-1Ba-L or HIV-1LAI; proviral DNA was then amplified by PCR in cells exposed to either virus, though coculture with lymphocytes rescued only HIV-1Ba-L. Altogether, these data indicate that macrophages are the major targets of HIV in cultured stromal layers. As virus replication in macrophages did not affect the profile of major cytokines involved in regulating hematopoiesis, HIV infection could alter hematopoiesis by other as yet unspecified mechanisms.     

Study of photosensitive mixtures of TMAE and helium, hydrocarbon or CF4-based carrier gases

Among the photocathodes used for particle identification based on the Cherenkov Ring Imaging technique, the TMAE molecule is still the best in terms of quantum efficiency. Despite the fact that TMAE gaseous photocathodes have already been used in a number of large experiments, one still seeks answers to many detailed questions. We present a systematic study of gaseous photocathodes based on TMAE mixed with helium, hydrocarbon and CF₄-based gases at normal pressure. The study includes a measurement of the electron drift velocity, gas quenching properties, single electron pulse height spectra and anode wire aging. The paper makes recommendations for carrier gas mixtures to obtain the best quenching, and suggests how to manage TMAE wire aging. This study was motivated by a specific particle identification detector proposal, the Fast Drift CRID proposed for the B-factory at SLAC.     

Increasing the interference immunity of broadband systems for measuring and transmitting information by utilizing nonlinear signal processing methods

A method is considered for increasing the immunity from interference of broadband systems for measuring and transmitting information. It is based on utilizing nonlinear methods to process spread-spectrum signals. The possibility is investigated of using a quasioptimal receiving device which can be implemented in practice. It is shown that the proposed method makes it possible to solve the rejection problem at the physical level. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 13–15, November, 1996.     

New ceramer high optical abrasion resistant transparent coating materials based on functionalized melamine and a tris(m-aminophenyl)phosphine oxide compound

Summary The synthesis of new high optical abrasion resistance coating materials has been undertaken by functionalizing melamine and tris(m-aminophenyl)phosphine oxide with a triethoxysilane containing reagent. These highly functionalized compounds have been used for coating a bis-phenol-A polycarbonate substrate by the sol-gel method. Preliminary data shows the abrasion resistance of the polymer substrate is considerably improved when it is coated by these optically clear materials.     

Afterburner [network-independent card for protocols]

Many current implementations of protocols such as the Transmission Control Protocol/Internet Protocol (TCP/IP) are inefficient because data are often accessed more frequently than necessary. Three techniques that reduce the need for memory bandwidth are proposed. The techniques are copy-on-write, page remapping, and single-copy. Afterburner, a network-independent card that provides the services that are necessary for a single-copy protocol stack, is described. The card has 1 MByte of local buffers and provides a simple interface to a variety of network link adapters, including HIPPI and asynchronous transfer mode (ATM). Afterburner can support transfers to and from the link adapter card at rates up to 1 Gbit/s. An implementation of TCP/IP that uses the features provided by Afterburner to reduce the movement of data to a single copy is discussed. Measurements of the end-to-end performance of Afterburner and the single-copy implementation of TCP/IP are presented     

Radon as a risk factor for extra-pulmonary tumours

Most divers and diving medicine specialists know that application of normobaric oxygen as first aid after a bubble disease incident is highly effective. However, as yet technical difficulties acted as a deterrent to using normobaric oxygen at the diving site. This can now be overcome by a newer technique. To be efficient, any therapy of bubble disease should follow three main principles: maximal partial pressure of inhaled oxygen (i.e. 100 kpa in normobaric, and 280 kpa in hyperbaric conditions); minimal partial pressure of inhaled nitrogen, which should ideally be near zero; immediate start of therapy, if possible at the diving site, but not later than 2 hours after the onset of the first symptoms. However, it has to be borne in mind that for an efficient normobaric oxygenation (100%), the standard apparatus design without oxygen reservoir is obsolete, for it offers at most 40% oxygen to the lungs. Currently the following technical approaches for an efficient normobaric oxygenation are available: open one-way systems with tightly fitting mask and oxygen reservoir bag (type Ambu or Leardal, etc.); open systems with on-demand regulation and tightly fitting mouth piece (type SCUBA, or Bird-respirator); closed systems with CO2 absorber (type oxygen rebreathing diving gear). The closed system is a genuine technical advance, because it needs 15 times less oxygen than open systems (about 90 liters oxygen for a 3-hours oxygenation run). Such an apparatus is thus of light weight, far less cumbersome, and nevertheless highly efficient. The therapy should start immediately at the site of the mishap and be maintained during the transport to the next HBO-unit (usually 3 to 6 hours).(ABSTRACT TRUNCATED AT 250 WORDS)