California Institute of Technology

About: California Institute of Technology is a education organization based out in Pasadena, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 57649 authors who have published 146691 publications receiving 8620287 citations. The organization is also known as: Caltech & Cal Tech.

Clock Mutants of Drosophila melanogaster

Abstract: Three mutants have been isolated in which the normal 24-hour rhythm is drastically changed. One mutant is arrhythmic; another has a period of 19 hr; a third has a period of 28 hr. Both the eclosion rhythm of a population and the locomotor activity of individual flies are affected. All these mutations appear to involve the same functional gene on the X chromosome.

Simple 'neural' optimization networks: An A/D converter, signal decision circuit, and a linear programming circuit

Abstract: We describe how several optimization problems can be rapidly solved by highly interconnected networks of simple analog processors. Analog-to-digital (A/D) conversion was considered as a simple optimization problem, and an A/D converter of novel architecture was designed. A/D conversion is a simple example of a more general class of signal-decision problems which we show could also be solved by appropriately constructed networks. Circuits to solve these problems were designed using general principles which result from an understanding of the basic collective computational properties of a specific class of analog-processor networks. We also show that a network which solves linear programming problems can be understood from the same concepts.

High-redshift galaxies in the hubble deep field : colour selection and star formation history to z 4

Abstract: The Lyman decrement associated with the cumulative effect of H I in QSO absorption systems along the line of sight provides a distinctive feature for identifying galaxies at z ≳ 2.5. Colour criteria, which are sensitive to the presence of a Lyman continuum break superposed on an otherwise flat UV spectrum, have been shown, through Keck spectroscopy, to successfully identify a substantial population of star-forming galaxies at 3 ≲ z ≲ 3.5. Such objects have proven to be surprisingly elusive in field galaxy redshift surveys; quantification of their surface densities and morphologies is crucial for determining how and when galaxies formed. The Hubble Deep Field (HDF) observations offer the opportunity to exploit the ubiquitous effect of intergalactic absorption and obtain useful statistical constraints on the redshift distribution of galaxies to considerably fainter limits than the current spectroscopic limits. We model the H I cosmic opacity as a function of redshift, including scattering in resonant lines of the Lyman series and Lyman continuum absorption, and use stellar population synthesis models with a wide variety of ages, metallicities, dust contents and redshifts to derive colour selection criteria that provide a robust separation between high-redshift and low-redshift galaxies. From the HDF images we construct a sample of star-forming galaxies at 2 ≲z ≲ 4.5. While none of the ∼ 60 objects in the HDF having known Keck/Low-Resolution Imaging Spectrograph (LRIS) spectroscopic redshifts in the range 0 ≲ z ≲1.4 is found to contaminate our high-redshift sample, our colour criteria are able to efficiently select the 2.6 ≲ z ≲ 3.2 galaxies identified by Steidel et al. The ultraviolet (and blue) dropout technique opens up the possibility of investigating cosmic star and element formation in the early Universe. We set a lower limit to the ejection rate of heavy elements per unit comoving volume from Type II supernovae at 〈z〉 = 2.75 of ≈ 3.6 × 10^(−4) M_⊙ yr^(−1) Mpc^(−3) (for q_0 = 0.5 and H_0 = 50 km s^(−1) Mpc^(−1)), which is 3 times higher than the local value but still 4 times lower than the rate observed at z ≈ 1. At 〈z〉 = 4, our lower limit to the cosmic metal ejection rate is ≈ 3 times lower than the 〈z〉 = 2.75 value. We discuss the implications of these results on models of galaxy formation, and on the chemical enrichment and ionization history of the intergalactic medium.

Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity

Abstract: Cavity quantum electrodynamics (QED) systems allow the study of a variety of fundamental quantum-optics phenomena, such as entanglement, quantum decoherence and the quantum–classical boundary. Such systems also provide test beds for quantum information science. Nearly all strongly coupled cavity QED experiments have used a single atom in a high-quality-factor (high-Q) cavity. Here we report the experimental realization of a strongly coupled system in the solid state: a single quantum dot embedded in the spacer of a nanocavity, showing vacuum-field Rabi splitting exceeding the decoherence linewidths of both the nanocavity and the quantum dot. This requires a small-volume cavity and an atomic-like two-level system. The photonic crystal slab nanocavity—which traps photons when a defect is introduced inside the two-dimensional photonic bandgap by leaving out one or more holes—has both high Q and small modal volume V, as required for strong light–matter interactions. The quantum dot has two discrete energy levels with a transition dipole moment much larger than that of an atom, and it is fixed in the nanocavity during growth.