摘要:

A brief comment on some of the newer developments in optical materials is presented. Then, a FTIR and Raman analysis of the evolution of TEOS‐based materials as a function of the heat treatment is shown and the change in morphology of these materials is explained supported on these spectra. Finally, the use of TEOS‐based glasses as matrices for optically‐active Eu3+probe is described.

ISSN:0094-243X    

DOI:10.1063/1.48805

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The unique features of fibre optic sensors have sparked wide spread interest in applications that provide new sensor capabilities or offer cost or performance benefits over existing sensors. Photonic sensors are small, lightweight, electrically passive, and immune to electromagnetic interference, making them attractive for industrial, ocean, military, and medical applications. Many of the attributes of optical sensing can be and are being applied today in a wide spectrum of applications areas. However, the oceans and the human body present many challenges in bringing optical sensing to these unique environments.

ISSN:0094-243X    

DOI:10.1063/1.48806

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An overview of the various ways in which hydrogen (H) interacts with different forms of silicon (Si) is presented. First‐principles theory has contributed significantly to our understanding of these phenomena. For crystalline silicon, the discussion encompasses H in solid solution, H diffusion, H interactions with deep and shallow levels, and H on the surface. The structure and energetics of Si‐H bonds are relevant for modeling the role of hydrogen in amorphous silicon. For polycrystalline silicon, the interactions of hydrogen with grain boundaries and, in particular, the insertion of H into strained Si‐Si bonds are addressed. A final topic concerns the role of hydrogen in silicon‐based layered structures, which play a role in light emission from porous silicon.

ISSN:0094-243X    

DOI:10.1063/1.48807

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new and highly sensitive method is described forinvivoandinsitustudies of photosynthetic activity of undetached leaves based on the photoacoustic effect. The general utility of this simple photothermal method is illustrated by examining the spectroscopy and photosynthetic activity of green, striped, and albino plants of maize. The technique is also used to show that the oxygen evolution in hybrids is higher than in inbred lines of maize.

ISSN:0094-243X    

DOI:10.1063/1.48808

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have used Scanning Tunneling Microscopy (STM) to study dopants, point defects, and interfaces in compound semiconductors after cleavage in Ultra‐High‐Vacuum. Features due to SiGadonors and ZnGaacceptors in the STM images of n+GaAs and p+GaAs have been identified and characterized on an atomic scale. For the first time, we found the spherical and triangle‐shape delocalized SiGadonor and ZnGaacceptor features, respectively. In heavily doped n+GaAs, Ga vacancies were observed that produce characteristic dark delocalized spherical features. The Ga vacancies tend to locate close to SiGadonors. We imaged an antisite defect in n+GaAs. High resolution STM spectroscopic images revealed very rich detail of the electronic structures of that site. Isoelectronic In and Ga elements in In0.2Ga0.8alloy were also identified. This allowed us to investigate the interfaces of GaAs/In0.2Ga0.8As/GaAs strained layer quantum wells atom‐by‐atom. Segregation of In at the In0.2Ga0.8As/GaAs interface and clustering inside In0.2Ga0.8As were studied.

ISSN:0094-243X    

DOI:10.1063/1.48809

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The hot big‐bang cosmology provides a reliable accounting of the Universe from about 10−2sec after the bang until the present, as well as a robust framework for speculating back to times as early as 10−43sec. Cosmology faces a number of important challenges; foremost among them are determining the quantity and composition of matter in the Universe and developing a detailed and coherent picture of how structure (galaxies, clusters of galaxies, superclusters, voids, great walls, and so on) developed. At present there is a working hypothesis—cold dark matter—which is based upon inflation and which, if correct, would extend the big bang model back to 10−32sec and cast important light on the unification of the forces. Many experiments and observations, from CBR anisotropy experiments to Hubble Space Telescope observations to experiments at Fermilab and CERN, are now putting the cold dark matter theory to the test. At present it appears that the theory is viable only if the Hubble constant is smaller than current measurements indicate (around 30 km s−1Mpc−1), or if the theory is modified slightly, e.g., by the addition of a cosmological constant, a small admixture of hot dark matter (5 eV ‘‘worth of neutrinos’’), more relativistic particle or a tilted spectrum of density perturbations.

ISSN:0094-243X    

DOI:10.1063/1.48810

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

As a collaboration between the National Radio Astronomy Observatory of the USA and the Instituto de Astronomi´a of the National University of Mexico with the financial support of CONACyT, Me´xico, nine receivers for the wavelength of 7 millimeters have been built and installed in the Very Large Array (VLA). These receivers extend up the frequency coverage and angular resolution of the VLA by a factor of two. Observations of a variety of astronomical sources, including H II regions, evolved stars, dust emission from young stellar objects, and quasars have been successfully achieved.

ISSN:0094-243X    

DOI:10.1063/1.48811

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Doing astronomy with photons of energies in excess of a GeV has turned out to be extremely challenging. Efforts are underway to develop instruments that may push astronomy to wavelengths smaller than 10−14cm by mapping the sky using high energy neutrinos instead. Neutrino astronomy, born with the identification of thermonuclear fusion in the sun and the particle processes controlling the fate of a nearby supernova, will reach outside the galaxy and make measurements relevant to cosmology. The field is immersed in technology in the domains of particle physics to which many of its research goals are intellectually connected. To mind come the search for neutrino mass, cold dark matter (supersymmetric particles?) and the monopoles of the Standard Model. While a variety of collaborations are pioneering complementary methods by building telescopes with effective area in excess of 0.01 km2, we show here that the natural scale of a high energy neutrino telescope is 1 km2. With several thousand optical modules and a price tag unlikely to exceed 100 million dollars, the scope of a kilometer‐scale instrument is similar to that of experiments presently being commissioned such as the SNO neutrino observatory in Canada and the Superkamiokande experiment in Japan.

ISSN:0094-243X    

DOI:10.1063/1.48812

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The South Pole Infrared Explorer is the name given a series of experiments to determine the suitability of the South Pole as a site for near infrared astrophysics observations. For the first phase of this project we have constructed a 60 cm telescope and a near infrared imaging spectrometer. With this instrumentation we plan to carry out a program of measurements to test the qualities of the site. We also plan to carry out a survey for faint galaxies. Between December of 1993 and February of 1994 we began to place the equipment at the Pole. Since then, the telescope and instrumentation have survived their first winter of operation. In this paper we describe the experiments and our experiences.

ISSN:0094-243X    

DOI:10.1063/1.48813

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The cosmic microwave background (CMB) is one of only a few physically observable remnants of the early Universe. Studies of the spectrum, polarization and spatial distribution of the CMB can potentially lead to a detailed understanding of the processes that took place in the early Universe. Many of the outstanding cosmological questions regarding the age, contents, future, and large scale dynamics of the universe are addressed in these studies. In particular, measurements of the spatial anisotropy of the CMB are a very effective method for testing and constraining models of cosmic structure formation.

ISSN:0094-243X    

DOI:10.1063/1.48814

出版商:AIP    

年代:1995

数据来源: AIP