Caltech Authors
(24.207 recursos)
Repository of works by Caltech published authors.
Mostrando recursos 1 - 20 de 206
1.
A survey of models of network formation: stability and efficiency - Jackson, Matthew O.
I survey the recent literature on the formation of networks. I provide definitions of network games, a number of examples of models from the literature, and discuss some of what is known about the (in)compatibility of overall societal welfare with individual incentives to form and sever links.
2.
DC and millimeter-wave performance of watt-level barrier-intrinsic-n+ diode-grid frequency multiplier fabricated on III-V compound semiconductors - Hwu, R. J.; Sadwick, P.; Luhmann, Jr., N. C.; Rutledge, D. B.
This paper reports the fabrication and millimeter-wave performance of a new class of monolithic metal-semiconductor heterostructure devices, the Barrier- Intrinsic-N+ (BIN) diode-grid frequency multipliers, which are fabricated on III-V compound semiconductors. This work also involves the measurement of the DC and low frequency
electrical properties of the BIN diode-grid frequency multiplier. In addition, a new analytical model which accurately describes the structure has been developed and is presented for the first time.
3.
The Sporadic Meteoroid Complex and Spacecraft Risk - Wiegert, Paul; Vaubaillon, Jeremie
The meteoroid population in near-Earth space is typically broken down into two components: shower meteoroids which orbit in collimated streams, and the older sporadic meteoroids which have been dispersed into a much broader uncollimated distribution of orbits. The sporadic meteors dominate the meteoroid flux at Earth in the size range of those particles of the most of the risk to spacecraft (approximately 100 microns to 1 cm). We describe the results of numerical simulations of the sporadic meteoroid complex by full physical modeling of meteoroids from ejection from their parent body through their perturbation by planets and radiation forces though...
4.
A 19 GHz 0.5 mW 0.35 μm CMOS frequency divider with shunt-peaking locking-range enhancement - Wu, Hui; Hajimiri, Ali
A frequency divider is an essential building block and one of the major sources of power dissipation in widely-used frequency synthesizers. As the output frequency of the synthesizer increases, the trade-off between the speed and power dissipation of dividers becomes more critical. Narrow-band injection-locked frequency dividers (ILFD) dissipate a fraction of the energy stored in the tank, which is determined by the quality factor, Q, of the resonator, in every cycle. Therefore, they have fundamentally lower power dissipation than wide-band dividers. Due to their narrow-band nature, ILFDs work in a limited frequency range (locking range). In this paper, shunt-peaking is...
5.
Highly efficient frequency triplers in the millimeter wave region incorporating a back-to-back configuration of two varactor diodes - Hwu, R. J.; Sadwick, L. P.; Luhmann, N. C., Jr.; Rutledge, D. B.; Sokolich, M.
This paper reports on the recent development of monolithic frequency tripler array employing a back-to-back configuration of varactor diodes. Even harmonic idler
circuits are unnecessary in this design. Furthermore, no external dc bias is required. The arrangement results in highly efficient, easily-fabricated and inexpensive frequency triplers.
6.
Watt-level millimeter-wave monolithic diode-grid frequency multipliers - Hwu, R. J.; Jou, C. F.; Lam, W. W.; Lieneweg, U.; Streit, D. C.; Luhmann, N. C., Jr.; Maserjian, J.; Rutledge, D. B.
Monolithic planar arrays containing in excess of 1000 Schottky diodes have produced watt level output at 66 GHz in a doubler configuration in excellent agreement with large signal predictions of the frequency multiplication. Current efforts are concentrated on fabricating and developing arrays of novel barrier-intrinsic-N+ (BIN) diode which promise increased performance in tripler and quintupler configurations.
7.
A novel tuning technique for distributed voltage controlled oscillators - Wu, Hui; Hajimiri, Ali
A novel current-steering delay-balanced tuning technique for distributed voltage controlled oscillators (DVCO) is demonstrated. This tuning technique is used to design a DVCO operating at 10 GHz in a 0.35 μm CMOS technology. The DVCO is continuously tunable between 9.9 and 10.3 GHz. Special attention is paid to the layout issues for the high frequency design.
8.
The inclination angle and mass of the black hole in XTE J1118+480 - Gelino, Dawn M.; Balman, Solen; Kiziloglu, Umit; Yilmaz, Arda; Kalemci, Emrah; Tomsick, John A.
We have obtained optical and infrared photometry of the quiescent soft X-ray transient XTE J1118+480. In addition to optical and J-band variations, we present H- and Ks-band ellipsoidal variations for this system. We model the variations in all bands simultaneously with the WD98 light curve modeling code. The infrared colors of the secondary star in this system are consistent with those of a K7 V, while there is evidence for light from the accretion disk in the optical. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is...
9.
Solar energy conversion - Crabtree, George W.; Lewis, Nathan S.
If solar energy is to become a practical alternative to fossil fuels, we must have efficient ways to convert photons into electricity, fuel, and heat. The need for better conversion technologies is a driving force behind many recent developments in biology, materials, and especially nanoscience.
10.
The MIMO wiretap channel - Oggier, Frédérique; Hassibi, Babak
We study the MIMO wiretap channel, a MIMO broadcast channel where the transmitter sends some confidential information to one user which is a legitimate receiver, while the other user is an eavesdropper. Perfect secrecy is achieved when the transmitter and the legitimate receiver can communicate at some positive rate, while ensuring that the eavesdropper gets zero bits of information. In this paper, we compute the perfect secrecy capacity of the multiple antenna MIMO broadcast channel, where the number of antennas is arbitrary for both the transmitter and the two receivers. Our technique involves a careful study of a Sato-like upper...
11.
A coding scheme for wireless networks with multiple antenna nodes and no channel information - Oggier, Frédérique; Hassibi, Babak
In this paper, we present a coding strategy for wireless relay networks where the relay nodes are small devices with few resources, while the source and sink are equipped with multiple antennas to increase the transmission rate. We assume no channel knowledge at all, and the receiver decodes knowing none of the channel paths. This coding scheme uses distributed space-time coding techniques and is inspired by noncoherent differential space-time coding. It is shown to yield a diversity linear in the minimum number of transmit/receive antennas times the number of relays.
12.
Connecting gas dynamics and star formation histories in nearby galaxies: the VLA—ANGST survey - Ott, Jürgen; Skillman, Evan; Dalcanton, Julianne; Walter, Fabian; Stilp, Adrienne; Koribalski, Bärbel; West, Andrew; Warren, Steven
In recent years, HST revolutionized the field of star formation in nearby galaxies. Due to its high angular resolution it has now become possible to construct star formation histories of individual stellar populations on scales of a few arcseconds spanning a range of up to ~600 Myr. This method will be applied to the ANGST galaxies, a large HST volume limited survey to map galaxies up to distances of 3.5–4.0 Mpc (excluding the Local Group). The ANGST sample is currently followed-up by high, ~6" resolution VLA observations of neutral, atomic hydrogen (HI) in the context of VLA-ANGST, an approved Large...
13.
The EVLA: prospects for HI - Ott, Jürgen; Perley, Rick; Rupen, Michael
To continue the unparalleled success of the Very Large Array (VLA) for radio astronomy, the facility is currently being converted to become the 'Expanded VLA' (EVLA). The EVLA will radically improve the VLA in order to cover the full 0.93–50 GHz radio wavelength range without gaps, provide up to an order of magnitude better sensitivity, and to allow observations at much larger bandwidths and spectral resolution as currently possible. For observations of the 21 cm line of atomic neutral hydrogen (HI), the EVLA offers thousands of km s^−1 velocity coverage at sub-km s^−1 resolution for targeted observations as well as...
14.
STEREO and ACE observations of CIR particles - Leske, R. A.; Mewaldt, R. A.; Mason, G. M.; Cohen, C. M. S.; Cummings, A. C.; Davis, A. J.; Labrador, A. W.; Miyasaka, H.; Stone, E. C.; Wiedenbeck, M. E.; von Rosenvinge, T. T.
In the present solar minimum, corotating interaction regions (CIRs) produce frequent particle enhancements at 1 AU as observed at STEREO and ACE. As the two STEREO spacecraft move apart, differences in CIR time profiles observed at each spacecraft are becoming large. The timing differences are often roughly similar to the corotation time lag between the two spacecraft, however many of the features seen at Ahead and Behind require more than just a time shift. Perhaps transient disturbances in the solar wind affect connection to or transport from the shock, or temporal changes occur in the CIR shock itself. Additional timing...
15.
Seed populations for large solar particle events of cycle 23 - Desai, M. I.; Mason, G. M.; Gold, R. E.; Krimigis, S. M.; Cohen, C. M. S.; Mewaldt, R. A.; Dwyer, J. R.; Mazur, J. E.
Using high-resolution mass spectrometers on board the Advanced Composition Explorer (ACE), we surveyed the event-averaged ~0.1-60 MeV/nuc heavy ion elemental composition in 64 large solar energetic particle (LSEP) events of cycle 23. Our results show the following: (1) The rare isotope ^3He is greatly enhanced over the corona or the solar wind values in 46% of the events. (2) The Fe/O ratio decreases with increasing energy up to ~10 MeV/nuc in ~92% of the events and up to ~60 MeV/nuc in ~64% of the events. (3) Heavy ion abundances from C-Fe exhibit systematic M/g-dependent enhancements that are remarkably similar to...
16.
New approaches to object classification in synoptic sky surveys - Donalek, C.; Mahabal, A.; Djorgovski, S. G.; Marney, S.; Drake, A.; Glikman, E.; Graham, M. J.; Williams, R.
Digital synoptic sky surveys pose several new object classification challenges. In surveys where real-time detection and classification of transient events is a science driver, there is a need for an effective elimination of instrument-related artifacts which can masquerade as transient sources in the detection pipeline, e.g., unremoved large cosmic rays, saturation trails, reflections, crosstalk artifacts, etc. We have implemented such an Artifact Filter, using a supervised neural network,
for the real-time processing pipeline in the Palomar-Quest (PQ) survey. After the training phase, for each object it takes as input a set of measured morphological parameters and returns the probability of...
17.
What's cool about hot stars? Infrared observations of cataclysmic variables with the Spitzer Space Telescope - Hoard, D. W.; Wachter, S.; Brinkworth, C. S.; Kafka, S.; Howell, S. B.; Ciardi, D. R.
Cataclysmic variables have been extensively observed at optical, ultraviolet, and Xray
wavelengths, where their white dwarf primary stars and bright accretion disks dominate their
emitted luminosity. Comparatively little is known about the infrared properties of cataclysmic variables.
The assumption that infrared observations would reveal only the “uninteresting” secondary
star has been shown to be false: recent infrared observations of cataclysmic variables have instead
shown that cool dust in these interacting binaries is possibly the most important contributor to
their spectral energy distributions at long wavelengths. We present recent results from infrared
observations of the cataclysmic variable EF Eridani obtained with the Spitzer Space Telescope.
18.
Elemental and isotopic fractionation in 3He-rich solar energetic particle events - Wiedenbeck, M. E.; Leske, R. A.; Cohen, C. M. S.; Cummings, A. C.; Mewaldt, R. A.; Stone, E. C.; von Rosenvinge, T. T.
Using data from the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE) mission, heavy ion composition measurements have been made in 26^3He-rich solar energetic particle (SEP) events that occurred between 1998 and 2004. Relative abundances of 13 elements from C through Ni have been investigated, as have the isotopic compositions of the elements Ne and Mg. We find a general tendency for the abundances to follow trends similar to those found in gradual SEP events, in which fractionation can be represented in the form of a power-law in Q/M. However several deviations from this pattern are noted that...
19.
Spitzer Space Telescope observations of low mass X-ray binaries - Wachter, Stefanie
We present preliminary results from our archival Spitzer Space Telescope program aimed at characterizing the mid-IR properties of compact objects, both isolated and in binary systems, i.e. white dwarfs, X-ray binaries, cataclysmic variables, and magnetars. Most of these sources are too faint at mid-IR wavelengths to be observable from the ground, so this study provides the very first comprehensive look at the mid-IR emission of these objects. Here we present our results for the low mass X-ray binaries. We considered all of the systems listed in the most recent catalog of Liu et al. (2007) that have known optical counterparts....
20.
Applications of quantum stochastic processes in quantum optics - Bouten, Luc
These lecture notes provide an introduction to quantum filtering and its applications in quantum optics. We start with a brief introduction to quantum probability, focusing on the spectral theorem. Then we introduce the conditional expectation and quantum stochastic calculus. In the last part of the notes we discuss the filtering problem.
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