A Noninvasive Optical Probe for Detecting Electrical Signals in Silicon IC’s

We report using a 1.3µm(silicon-sub-bandgap) optical probing system to detect electrical signals in silicon integrated circuits. Free carriers within integrated active devices perturb the index of refraction of the material, and we have used a Nomarski interferometer to sense this perturbation. Typical charge-density modulation in active devices produces a substantial index perturbation, and because of this, we have used an InGaAsP semiconductor laser to experimentally observe real-time 0.8V digital signals applied to a bipolar transistor. These signals were detected with a signal-to-noise ratio of 20dB in a system detection bandwidth of over 200MHz. Since the free-carrier-induced refractive-index perturbation is present in all semiconductor materials, in the future, we expect to be able to detect signals in integrated circuits fabricated in GaAs or any other material, and by taking advantage of the high spatial and temporal resolution of this system, we should be able to observe free-carrier dynamics within most active devices

Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions

We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard's Star. We obtain absolute parallax values for Proxima Cen pi_{abs} = 0.7687 arcsecond and for Barnard's Star pi_{abs} = 0.5454 arcsecond. Once low-amplitude instrumental systematic errors are identified and removed, our companion detection sensitivity is less than or equal to one Jupiter mass for periods longer than 60 days for Proxima Cen. Between the astrometry and the radial velocity results we exclude all companions with M > 0.8M_{Jup} for the range of periods 1 < P < 1000 days. For Barnard's Star our companion detection sensitivity is less than or equal to one Jupiter mass for periods long er than 150 days. Our null results for Barnard's Star are consistent with those of Gatewood (1995).Comment: 35 pages, 13 figures, to appear in August 1999 A

Photometry of Proxima Centauri and Barnard's Star Using HST Fine Guidance Sensor 3: A Search for Periodic Variations

We have observed Proxima Centauri and Barnard's Star with Hubble Space Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 milli-magnitude internal photometric precision. We identify two distinct behavior modes over the past four years: higher amplitude, longer period; smaller amplitude, shorter period. Within the errors one period (P ~ 83d) is twice the other. Barnard's Star shows very weak evidence for periodicity on a timescale of approximately 130 days. If we interpret these periodic phenomena as rotational modulation of star spots, we identify three discrete spots on Proxima Cen and possibly one spot on Barnard's Star. We find that the disturbances change significantly on time scales as short as one rotation period.Comment: 39 pages, 17 figure

Constant Ciphertext-Rate Non-committing Encryption from Standard Assumptions

Non-committing encryption (NCE) is a type of public key encryption which comes with the ability to equivocate ciphertexts to encryptions of arbitrary messages, i.e., it allows one to find coins for key generation and encryption which “explain” a given ciphertext as an encryption of any message. NCE is the cornerstone to construct adaptively secure multiparty computation [Canetti et al. STOC’96] and can be seen as the quintessential notion of security for public key encryption to realize ideal communication channels. A large body of literature investigates what is the best message-to-ciphertext ratio (i.e., the rate) that one can hope to achieve for NCE. In this work we propose a near complete resolution to this question and we show how to construct NCE with constant rate in the plain model from a variety of assumptions, such as the hardness of the learning with errors (LWE), the decisional Diffie-Hellman (DDH), or the quadratic residuosity (QR) problem. Prior to our work, constructing NCE with constant rate required a trusted setup and indistinguishability obfuscation [Canetti et al. ASIACRYPT’17]

Effects of Policies Designed to Keep Firearms from High-Risk Individuals

This article summarizes and critiques available evidence from studies published between 1999 and August 2014 on the effects of policies designed to keep firearms from high-risk individuals in the United States. Some prohibitions for high-risk individuals (e.g., those under domestic violence restraining orders, violent misdemeanants) and procedures for checking for more types of prohibiting conditions are associated with lower rates of violence. Certain laws intended to prevent prohibited persons from accessing firearms -- rigorous permit-to-purchase, comprehensive background checks, strong regulation and oversight of gun dealers, and requiring gun owners to promptly report lost or stolen firearms -- are negatively associated with the diversion of guns to criminals. Future research is needed to examine whether these laws curtail nonlethal gun violence and whether the effects of expanding prohibiting conditions for firearm possession are modified by the presence of policies to prevent diversion

The Distance To The Hyades Cluster Based On Hubble Space Telescope Fine Guidance Sensor Parallaxes

Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.NASA HST GTO, HF-1042.01-93A, HF-1046.01-93A, NAS526555Astronom

A Logical Model Provides Insights into T Cell Receptor Signaling

Cellular decisions are determined by complex molecular interaction networks. Large-scale signaling networks are currently being reconstructed, but the kinetic parameters and quantitative data that would allow for dynamic modeling are still scarce. Therefore, computational studies based upon the structure of these networks are of great interest. Here, a methodology relying on a logical formalism is applied to the functional analysis of the complex signaling network governing the activation of T cells via the T cell receptor, the CD4/CD8 co-receptors, and the accessory signaling receptor CD28. Our large-scale Boolean model, which comprises 94 nodes and 123 interactions and is based upon well-established qualitative knowledge from primary T cells, reveals important structural features (e.g., feedback loops and network-wide dependencies) and recapitulates the global behavior of this network for an array of published data on T cell activation in wild-type and knock-out conditions. More importantly, the model predicted unexpected signaling events after antibody-mediated perturbation of CD28 and after genetic knockout of the kinase Fyn that were subsequently experimentally validated. Finally, we show that the logical model reveals key elements and potential failure modes in network functioning and provides candidates for missing links. In summary, our large-scale logical model for T cell activation proved to be a promising in silico tool, and it inspires immunologists to ask new questions. We think that it holds valuable potential in foreseeing the effects of drugs and network modifications

Atmospheric Density Uncertainty Quantification for Satellite Conjunction Assessment

Conjunction assessment requires knowledge of the uncertainty in the predicted orbit. Errors in the atmospheric density are a major source of error in the prediction of low Earth orbits. Therefore, accurate estimation of the density and quantification of the uncertainty in the density is required. Most atmospheric density models, however, do not provide an estimate of the uncertainty in the density. In this work, we present a new approach to quantify uncertainties in the density and to include these for calculating the probability of collision Pc. For this, we employ a recently developed dynamic reduced-order density model that enables efficient prediction of the thermospheric density. First, the model is used to obtain accurate estimates of the density and of the uncertainty in the estimates. Second, the density uncertainties are propagated forward simultaneously with orbit propagation to include the density uncertainties for Pc calculation. For this, we account for the effect of cross-correlation in position uncertainties due to density errors on the Pc. Finally, the effect of density uncertainties and cross-correlation on the Pc is assessed. The presented approach provides the distinctive capability to quantify the uncertainty in atmospheric density and to include this uncertainty for conjunction assessment while taking into account the dependence of the density errors on location and time. In addition, the results show that it is important to consider the effect of cross-correlation on the Pc, because ignoring this effect can result in severe underestimation of the collision probability.Comment: 15 pages, 6 figures, 5 table

Photometry of Proxima Centauri and Barnard\u27s Star Using Hubble Space Telescope Fine Guidance Sensor 3: A Search for Periodic Variations

We have observed Proxima Centauri and Barnard\u27s star with the Hubble Space Telescope Fine Guidance Sensor 3. Proxima Cen exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 mmag internal photometric precision. We identify two distinct behavior modes over the past 4 years: higher amplitude, longer period and smaller amplitude, shorter period. Within the errors, one period (P ~ 83 days) is twice the other. Barnard\u27s star shows very weak evidence for periodicity on a timescale of approximately 130 days. If we interpret these periodic phenomena as rotational modulation of starspots, we identify three discrete spots on Proxima Cen and possibly one spot on Barnard\u27s star. We find that the disturbances change significantly on timescales as short as one rotation period