Repository of works by Caltech published authors.
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Gaze bias both reflects and influences preference - Shimojo, Shinsuke; Simion, Claudiu; Shimojo, Eiko; Scheier, Christian
Emotions operate along the dimension of approach and aversion, and it is reasonable to assume that orienting behavior is intrinsically linked to emotionally involved processes such as preference decisions. Here we describe a gaze 'cascade effect' that was present when human observers were shown pairs of human faces and instructed to decide which face was more attractive. Their gaze was initially distributed evenly between the two stimuli, but then gradually shifted toward the face that they eventually chose. Gaze bias was significantly weaker in a face shape discrimination task. In a second series of experiments, manipulation of gaze duration, but...
Molecular physiology of P2X receptors and ATP signalling at synapses - Khakh, Baljit S.
ATP is found in every cell, where it is a major source of energy. But in the nervous system, ATP also has additional actions, which include its role in fast synaptic transmission and modulation. Here I discuss the 'fast' actions of ATP at synapses, the properties of the receptors that are activated by ATP and the physiology of ATP signalling, with emphasis on its role in pain processing.
Nucleotide binding by the histidine kinase CheA - Bilwes, Alexandrine M.; Quezada, Cindy M.; Croal, Laura R.; Crane, Brian R.; Simon, Melvin I.
To probe the structural basis for protein histidine kinase (PHK) catalytic activity and the prospects for PHK-specific inhibitor design, we report the crystal structures for the nucleotide binding domain of Thermotoga maritima CheA with ADP and three ATP analogs (ADPNP, ADPCP and TNP-ATP) bound with either Mg2+ or Mn2+. The conformation of ADPNP bound to CheA and related ATPases differs from that reported in the ADPNP complex of PHK EnvZ. Interactions of the active site with the nucleotide bold gamma-phosphate and its associated Mg2+ ion are linked to conformational changes in an ATP-lid that could mediate recognition of the substrate...
Programmed population control by cell-cell communication and regulated killing - You, Lingchong; Cox, Robert Sidney, III; Weiss, Ron; Arnold, Frances H.
De novo engineering of gene circuits inside cells is extremely difficult, and efforts to realize predictable and robust performance must deal with noise in gene expression and variation in phenotypes between cells. Here we demonstrate that by coupling gene expression to cell survival and death using cell–cell communication, we can programme the dynamics of a population despite variability in the behaviour of individual cells. Specifically, we have built and characterized a ‘population control’ circuit that autonomously regulates the density of an Escherichia coli population. The cell density is broadcasted and detected by elements from a bacterial quorum-sensing system, which in...
Science for the have-nots - Developed and developing nations can build better partnerships - Zewail, Ahmed H.
Only a fifth of the population enjoys the benefit of life in the 'developed world', and the gap between the haves and have-nots continues to increase, threatening stability. According to the World Bank, of the 6 billion people on Earth, 4.8 billion live in developing countries, 3 billion live on less than US$2 a day, and 1.2 billion live on less than $1 a day, which defines the absolute poverty standard; 1.5 billion people do not have access to clean water.
State-dependent cross-inhibition between transmitter-gated cation channels - Khakh, Baljit S.; Zhou, Xiaoping; Sydes, Jason; Galligan, James J.; Lester, Henry A.
Transmitter-gated cation channels are detectors of excitatory chemical signals at synapses in the nervous system. Here we show that structurally distinct α3β4 nicotinic and P2X_2 channels influence each other when co-activated. The activation of one channel type affects distinct kinetic and conductance states of the other, and co-activation results in non-additive responses owing to inhibition of both channel types. State-dependent inhibition of nicotinic channels is revealed most clearly with mutant P2X_2 channels, and inhibition is decreased at lower densities of channel expression. In synaptically coupled myenteric neurons, nicotinic fast excitatory postsynaptic currents are occluded during activation of endogenously co-expressed P2X...
Light work with water - Lewis, Nathan S.
Sunlight can be harnessed by semiconductors to generate a fuel, hydrogen gas, from water. This approach will be impracticable until certain materials-related constraints are overcome: photochemists are on the case.
New Year's wishes: All I want for 2005 is... - Baltimore, David
Students, scholars and at least one Nobel prizewinner have had trouble getting into the United States this year, thanks to immigration rules that have grown ever tighter since the terrorist attacks of 11 September 2001. Zhores Alferov, who won the 2000 Nobel Prize in Physics for his work on semiconductors, stormed out of the US consulate in St Petersburg, Russia, this September without his visa after being grilled about the nature of his work.
Signal transduction - A cellular rescue team - Pomerantz, Joel L.; Baltimore, David
A protein called glycogen synthase kinase-3β is already known to participate in early embryonic development and cell-fate determination. Now it seems that the protein is also involved in a cell's decision to live or die.
Ordered porous materials for emerging applications - Davis, Mark E.
"Space—the final frontier." This preamble to a well-known television series captures the challenge encountered not only in space travel adventures, but also in the field of porous materials, which aims to control the size, shape and uniformity of the porous space and the atoms and molecules that define it. The past decade has seen significant advances in the ability to fabricate new porous solids with ordered structures from a wide range of different materials. This has resulted in materials with unusual properties and broadened their application range beyond the traditional use as catalysts and adsorbents. In fact, porous materials now...
Electronics in a spin - Roukes, Michael L.
Electrons can be shuttled around according to their 'spin', as well as their charge. Do this efficiently in a semiconductor and the future of electronics starts to look very different.
Ultralow-threshold Raman laser using a spherical dielectric microcavity - Spillane, S. M.; Kippenberg, T. J.; Vahala, K. J.
The ability to confine and store optical energy in small volumes has implications in fields ranging from cavity quantum electrodynamics to photonics. Of all cavity geometries, micrometre-sized dielectric spherical resonators are the best in terms of their ability to store energy for long periods of time within small volumes. In the sphere, light orbits near the surface, where long confinement times (high Q) effectively wrap a large interaction distance into a tiny volume. This characteristic makes such resonators uniquely suited for studies of nonlinear coupling of light with matter. Early work recognized these attributes through Raman excitation in microdroplets—but microdroplets...
Measurement of Prompt ψ(2S) to J=ψ Yield Ratios in Pb-Pb and p-p Collisions at √sNN = 2.76 TeV - Khachatryan, V.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Wilkinson, R.; Xie, S.; Zhu, R. Y.
The ratio between the prompt ψ(2S) and J/ψ yields, reconstructed via their decays into μ^+μ^−, is measured in Pb-Pb and p-p collisions at √sNN = 2.76 TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150 μb^(−1) and 5.4 pb^(−1), respectively. The double ratio of measured yields (Nψ_((2S))/N_(J/ψ))_(Pb−Pb)/(N_(ψ(2S))/N_(J/ψ))_(p−p) is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, |y|<1.6, covering the transverse momentum range 6.5< p_T <30 GeV/c, and the other at forward rapidity, 1.6< |y| <2.4, extending to lower p_T values, 3< p_T...
Study of Vector Boson Scattering and Search for New Physics in Events with Two Same-Sign Leptons and Two Jets - Khachatryan, V.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Duarte, J.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Vlimant, J. R.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Dubinin, M.
A study of vector boson scattering in pp collisions at a center-of-mass energy of 8 TeV is presented. The data sample corresponds to an integrated luminosity of 19.4 fb^(−1) collected with the CMS detector. Candidate events are selected with exactly two leptons of the same charge, two jets with large rapidity separation and high dijet mass, and moderate missing transverse energy. The signal region is expected to be dominated by electroweak same-sign W-boson pair production. The observation agrees with the standard model prediction. The observed significance is 2.0 standard deviations, where a significance of 3.1 standard deviations is expected based on...
Astronomy - The missing link - Kulkarni, Shri
Some stars might be 'magnetars', powered by magnetism instead of fusion. The discovery of an X-ray burst from an anomalous X-ray pulsar suggests that this type of star can be added to the list.
Extinction of the dinosaurs: A 1982 understanding - Schopf, Thomas J. M.
The objective record appears to be that the dinosaur fauna of the latest Maastrichtian (i.e., latest Cretaceous) was chiefly (and perhaps exclusively) restricted to the Western Interior Seaway of the United States and southern Canada and included fewer than 20 species distributed among approximately 15 genera and 10 families. In the late Maastrichtian, as has been known for many years, sea level went down by 150 to 200 m in the western interior. The interior seaway (along which the dinosaurs were living) dried up and seasonality increased and habitable area was reduced as widespread flood plains yielded to uplifted, restricted...
A note on the cohomology of the Langlands group - Fan, Edward S. T.; Flach, M.
We begin with a comparison of various cohomology theories for topological groups. Using the continuity result for Moore cohomology, we establish a Hochschild-Serre spectral sequence for a slightly larger class of groups. We use these properties to compute the cohomology of the Langlands group of a totally imaginary field. The appendix answers a question raised by Flach concerning the cohomological dimension of the group ℝ.
The interaction of the Cretaceous/Tertiary Extinction Bolide with the atmosphere, ocean, and solid Earth - O'Keefe, John D.; Ahrens, Thomas J.
The mechanics of large-scale (~10-km diameter) asteroidal, cometary, and meteoroid swarm impact onto a silicate Earth covered by water and a gas layer (atmosphere) demonstrate that only ~ 15% to ~ 5% of the energy of 15 to 45 km/s bolides is taken up directly during the passage through the ocean and atmosphere, respectively. Upon impact with the Earth, ~ 10 to 10^2 times the bolide mass of water or rock can be ejected to the stratosphere: however, only ~0.1 bolide masses is in < 1 μm particles. The vaporized, melted, and (< 1 mm) solid ejecta transfer up to...
Neurobiology: Snails, synapses and smokers - Dougherty, Dennis A.; Lester, Henry A.
The discovery of a protein that controls the transmission of nerve impulses in snails is significant in its own right. It also advances our understanding of the vertebrate neurotransmitter receptor that responds to nicotine.