Xenon-iodine dating: sharp isochronism in chondrites.

Measurements of the accumulation of Xe(l29) from radioactive decay of extinct 1(129) in meteorites show that the 1(129)/ 1(127) ratio in high-temperature minerals in diverse chondrites was 10(-4) at the time of cooling. The uniformity in the ratio indicates that the minerals cooled simultaneously within 1 or 2 million years.

Modulation of oscillatory neuronal synchronization by selective visual attention.

In crowded visual scenes, attention is needed to select relevant stimuli. To study the underlying mechanisms, we recorded neurons in cortical area V4 while macaque monkeys attended to behaviorally relevant stimuli and ignored distracters. Neurons activated by the attended stimulus showed increased gamma-frequency (35 to 90 hertz) synchronization but reduced low-frequency (<17 hertz) synchronization compared with neurons at nearby V4 sites activated by distracters. Because postsynaptic integration times are short, these localized changes in synchronization may serve to amplify behaviorally relevant signals in the cortex.

Plutonium-244: confirmation as an extinct radioactivity.

The mass spectrum of xenon from spontaneous fission in a laboratory sample of plutonium-244 is precisely what meteoriticists predicted it would be; this discovery completes a web of proof that this nuclide is a bona fide extinct radioactivity of galactic origin, that r-process nucleosynthesis was ongoing in the galaxy at the time of the birth of the sun, and that the early meteoritic abundances of plutonium-244, heretofore tentative, can be utilized with confidence in models for the chronology of galactic nucleosynthesis. The search for an explanation for anomalous fission-like xenon in carbonaceous chondrites can now be narrowed.

Isotopic analysis of rare gases from stepwise heating of lunar fines and rocks.

Highlights of a first effort in sorting out rare gases in lunar material are solar wind rare gases in abundance; variable (20)Ne/(22)Ne but constant (21)Ne/ (22)Ne ratios in fractions of the trapped neon; cosmogenic rare gases similar to those found in meteorites, except for copious (131)Xe in one rock but not in another; at Tranquillity Base a rock 4.1 x 10(9) years old which reached the surface 35 to 65 million years ago, amid soil whose particles have typically been within a meter of the surface for 10(9) years or more.

Attention! V1 neurons lining up for inspection.

In this issue of Neuron, Roelfsema and Spekreijse report that macaque V1 neuron responses are correlated with target choice in a task requiring monkeys to attentively trace a line to plan a saccade. These results provide evidence that V1 is actively involved in the interpretation of visual stimuli.

Attention increases sensitivity of V4 neurons.

When attention is directed to a location in the visual field, sensitivity to stimuli at that location is increased. At the neuronal level, this could arise either through a multiplicative increase in firing rate or through an increase in the effective strength of the stimulus. To test conflicting predictions of these alternative models, we recorded responses of V4 neurons to stimuli across a range of luminance contrasts and measured the change in response when monkeys attended to them in order to discriminate a target stimulus from nontargets. Attention caused greater increases in response at low contrast than at high contrast, consistent with an increase in effective stimulus strength. On average, attention increased the effective contrast of the attended stimulus by a factor of 1.51, an increase of 51% of its physical contrast.

Exogenous attentional selection of transparent superimposed surfaces modulates early event-related potentials.

Using a transparent motion paradigm, [Valdes-Sosa, M., Bobes, M. A., Rodriguez, V., & Pinilla, T. (1998). Switching attention without shifting the spotlight object-based attentional modulation of brain potentials, Journal of Cognitive Neuroscience, 10, 137-151; Valdes-Sosa, M., Cobo, A., & Pinilla, T. (2000). Attention to object files defined by transparent motion, Journal of Experimental Psychological: Human Perception and Performance, 26, 488-505] found that when attention is endogenously directed to one surface, observers can more reliably report the direction of a brief translation of the cued than the uncued surface. Using a similar design [Reynolds, J. H., Alborzian, S., & Stoner, G. R. (2003). Exogenously cued attention triggers competitive selection of surfaces, Vision Research, 43, 59-66] found that even in the absence of an endogenous cue, the first translation acted as a potent exogenous cue that impaired the observer's ability to discriminate a subsequent translation of the other surface. We investigated the neural basis of this exogenous cueing effect by recording visual event-related potentials (ERPs) elicited by translations of the cued and uncued surfaces. Subjects were given the task of judging whether or not the first and second translations were identical in direction, and their performance was impaired when the second translation occurred on the uncued, as compared to the cued surface. The posterior C1 (75-110 ms) and N1 (160-210 ms) components of the ERP elicited by the second translation of the cued surface were larger than those elicited by translation of the uncued surface. These behavioral and ERP cueing effects were present even when the two surfaces were identical in color and thus could not be attributed to attention-related modulations of the gain of color channels. These findings provide evidence that exogenous cueing results in preferential selection of the cued surface at both early and intermediate stages of visual-cortical processing.

Chemical and biological studies of a cigarette that heats rather than burns tobacco.

Cigarettes can be developed that heat rather than burn tobacco. Such products would be expected to have less "tar" and other combustion products than cigarettes that burn tobacco. With one product of this type, benzo(a)pyrene, N-nitrosamines, phenolic compounds, acetaldehyde, acrolein, hydrogen cyanide, and N-heterocyclic compounds have been reduced 10- to 100-fold compared to the Kentucky reference (1R4F) cigarette, a representative low-tar cigarette. The yields of nicotine and carbon monoxide from this new cigarette are less than the yields of 95% and 75%, respectively, of the cigarettes sold in the United States during 1988. Nicotine absorption from smoking this new cigarette is not significantly different from that of tobacco-burning cigarettes yielding equivalent levels of nicotine. The urine mutagenicity of smokers of new cigarettes is significantly less (P less than .05) than that of smokers of tobacco-burning cigarettes and is not significantly different (P greater than .10) from that of nonsmokers. We conclude that cigarettes which heat rather than burn tobacco can reduce the yield of tobacco combustion products. This simplification of smoke chemistry had no effect on nicotine absorption in smokers and resulted in a reduction of biological activity in smokers as measured by urine mutagenicity.

Dietary nicotine: a source of urinary cotinine.

Foods, principally from plants in the family Solanaceae, and a number of teas were examined for the presence of nicotine. Dietary nicotine would give rise to cotinine in urine and compromise estimates of exposure to tobacco smoke that depend on urinary cotinine. All foods were homogenized, extracted and analysed for nicotine and cotinine by gas chromatography with nitrogen-sensitive detection (GC) and/or GC/MS (mass spectrometry). Weak acid and aqueous extracts of the teas were analysed in a similar manner. Nicotine was not detected (less than 1 ng/ml of extract) in egg plant or green pepper. The average values for nicotine in tomato and potato were 7.3 ng/g wet weight and 15 ng/g wet weight, respectively. Black teas, including regular and decaffeinated brands, had nicotine contents ranging from non-detectable to greater than 100 ng/g wet weight. Instant teas yielded the highest nicotine contents observed (up to 285 ng/g wet weight). The possible sources of nicotine in these foods are discussed. A range of potential values for urinary cotinine concentrations (0.6 to 6.2 ng/ml) was calculated based upon estimated average and maximal consumptions of these foods and beverages. Because of the potential for exposure to nicotine by way of these routes, the use of urinary cotinine as a biomarker of exposure to environmental tobacco smoke may be compromised.

A fuzzy ARTMAP nonparametric probability estimator for nonstationary pattern recognition problems.

An incremental, nonparametric probability estimation procedure using the fuzzy ARTMAP (adaptive resonance theory-supervised predictive mapping) neural network is introduced. In the slow-learning mode, fuzzy ARTMAP searches for patterns of data on which to build ever more accurate estimates. In max-nodes mode, the network initially learns a fixed number of categories, and weights are then adjusted gradually.

Fuzzy ARTMAP: A neural network architecture for incremental supervised learning of analog multidimensional maps.

A neural network architecture is introduced for incremental supervised learning of recognition categories and multidimensional maps in response to arbitrary sequences of analog or binary input vectors, which may represent fuzzy or crisp sets of features. The architecture, called fuzzy ARTMAP, achieves a synthesis of fuzzy logic and adaptive resonance theory (ART) neural networks by exploiting a close formal similarity between the computations of fuzzy subsethood and ART category choice, resonance, and learning. Four classes of simulation illustrated fuzzy ARTMAP performance in relation to benchmark backpropagation and generic algorithm systems. These simulations include finding points inside versus outside a circle, learning to tell two spirals apart, incremental approximation of a piecewise-continuous function, and a letter recognition database. The fuzzy ARTMAP system is also compared with Salzberg's NGE systems and with Simpson's FMMC system.

Improved charcoal trap for rare gas mass spectrometry.

A charcoal trap for progressive desorption of rare gases, including helium and neon, is described and performance data given. Cooling is by a commercial helium expansion refrigerator. Temperatures are readily controlled down to about 20 K. No cold, condensed gases are used.

Combined analysis of tall fescue steer grazing studies in the Eastern United States.

The mixed-models procedure (MMP) was used to analyze pooled data sets from 12 independent studies conducted during the last 13 yr at nine locations in seven states to provide combined estimates of daily gains by beef steers (Bos taurus) grazing tall fescue (Festuca arundinacea Schreb.) pastures free of (E-) or infested (E+) at different levels with the endophytic fungus Acremonium coenophialum. Treatments included low-infestation (< or = 5% E+), moderate-infestation (> or = 20 to < or = 35% E+), and high-infestation (> or = 50 to < or = 97% E+) tall fescue pastures, and, in tall fescue-clover (Trifolium spp.) mixtures, pastures at the same E+ levels with approximately 25 and 10% clover in spring and summer stands, respectively. Spring, summer, and combined spring+summer data were analyzed separately. The MMP permitted estimation of the fixed effects of treatments over a broad inference space of future years and different tall fescue pastures over a wide geographic range; detected relationships that had not been apparent in the individual studies, such as the interactions between clover presence and E+ infestation levels; and provided a more coherent body of information than did the results obtained from each discrete study. Logistical and financial constraints that force undesirable compromises in the conduct of future grazing and other expensive or time-consuming research may be avoided by using MMP within the context of cooperative projects.

The effect of heating temperature and nitric acid treatments on the performance of Cu- and Zn-based broad spectrum respirator carbons.

Impregnated activated carbons (IACs) that are used in broad spectrum gas mask applications have historically contained copper and/or zinc impregnants. The addition of an oxidizing agent, such as nitric acid (HNO(3)) can be useful in distributing the metallic impregnants uniformly on the activated carbon substrate. In this work, we study IACs prepared from copper nitrate (Cu(NO(3))(2)) and zinc nitrate (Zn(NO(3))(2)) precursors as a function of HNO(3) content present in the impregnating solution and as a function of heating temperature. The gas adsorption capacity of the IACs was determined by dynamic flow testing using sulfur dioxide (SO(2)), ammonia (NH(3)), hydrogen cyanide (HCN) and cyclohexane (C(6)H(12)) challenge gases under dry and humid conditions. The thermal decomposition and distribution of the impregnant on the activated carbon substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis techniques. Relationships between gas adsorption capacity, impregnant distribution and the species of surface impregnants are discussed.

Pneumonia in the immunocompetent patient.

Pneumonia is an acute inflammation of the lower respiratory tract. Lower respiratory tract infection is a major cause of mortality worldwide. Pneumonia is most common at the extremes of life. Predisposing factors in children include an under-developed immune system together with other factors, such as malnutrition and over-crowding. In adults, tobacco smoking is the single most important preventable risk factor. The commonest infecting organisms in children are respiratory viruses and Streptoccocus pneumoniae. In adults, pneumonia can be broadly classified, on the basis of chest radiographic appearance, into lobar pneumonia, bronchopneumonia and pneumonia producing an interstitial pattern. Lobar pneumonia is most commonly associated with community acquired pneumonia, bronchopneumonia with hospital acquired infection and an interstitial pattern with the so called atypical pneumonias, which can be caused by viruses or organisms such as Mycoplasma pneumoniae. Most cases of pneumonia can be managed with chest radiographs as the only form of imaging, but CT can detect pneumonia not visible on the chest radiograph and may be of value, particularly in the hospital setting. Complications of pneumonia include pleural effusion, empyema and lung abscess. The chest radiograph may initially indicate an effusion but ultrasound is more sensitive, allows characterisation in some cases and can guide catheter placement for drainage. CT can also be used to characterise and estimate the extent of pleural disease. Most lung abscesses respond to medical therapy, with surgery and image guided catheter drainage serving as options for those cases who do not respond.

Investigation of copper oxide impregnants prepared from various precursors for respirator carbons.

Copper oxide impregnated activated carbon was prepared by three methods and studied as a respirator carbon. Using techniques such as dynamic flow testing, X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), copper oxide impregnants, derived from different sources such as basic copper carbonate (Cu(2)CO(3)(OH)(2)), copper nitrate (Cu(NO(3))(2)) and copper chloride (CuCl(2)) reacted with sodium hydroxide (NaOH), have been studied. Dynamic flow tests performed using sulfur dioxide (SO(2)), ammonia (NH(3)) and hydrogen cyanide (HCN) challenge gases allow the determination of the stoichiometric ratio of reaction (SRR) between challenge gas and impregnant. Thermal gravimetric analysis experiments showed that an inert heating environment was required when thermally decomposing the Cu(NO(3))(2) impregnant to CuO to avoid damaging the activated carbon substrate. SEM has been used to investigate dispersal and particle size of the impregnant on the activated carbon. XRD permits the identification of crystalline and amorphous phases as well as the grain size of the impregnant. XRD analysis of samples before and after exposure to SO(2) has allowed the active impregnant in SO(2) adsorption to be identified. The relationship between SRR, impregnant loading and grain size is discussed. Methods to improve impregnant distribution are presented and their impact discussed.

The investigation of copper-based impregnated activated carbons prepared from water-soluble materials for broad spectrum respirator applications.

The preparation of impregnated activated carbons (IACs) from aqueous, copper-containing solutions for broad spectrum gas filtration applications is studied here. Several samples were studied to determine the effect that impregnant loading, impregnant distribution and impregnant recipe had on the overall performance. Dynamic flow testing was used to determine the gas filtration capacity of the IAC samples versus a variety of challenge gases. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were used to characterize the impregnant distribution on the carbon as a function of impregnant loading. Oven tests were performed to determine the thermal stability of the IAC samples exposed to elevated temperatures. The role impregnant distribution plays in gas filtration capacity and the overall performance of the IAC samples is discussed. The IAC samples prepared in this work were found to have gas filtration capacities as good as or better than broad spectrum respirator carbon samples prepared from the patent literature. IACs impregnated with an aqueous 2.4 M Cu(NO(3))(2)/0.04 M H(3)PO(4).12MoO(3)/4M HNO(3) solution that were heated to 200 degrees C under argon were found to have the best overall performance of the samples studied in this work.