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We analyzed the interaction between the North American monsoon anticyclone (NAMA) and summertime cross‐tropopause convective outflow by applying a trajectory analysis to a climatology of convective overshooting tops (OTs) identified in GOES satellite images, which covers the domain from 29°S to 68°N and from 205 to 1.25°W for the time period of May through September 2013. With this analysis we identified seasonally, geographically, and altitude‐dependent variability in NAMA strength and in cross‐tropopause convection that control their interaction. We find that the NAMA has the strongest impact on the circulation of convectively influenced air masses in August. Over the entire time period examined the intertropical convergence zone contributes the majority of OTs with a larger fraction of total OTs at 370 K (on average 70%) than at 400 K (on average 52%). During August at 370 K, the convectively influenced air masses within the NAMA circulation, as determined by the trajectory analysis, are primarily sourced from the intertropical convergence zone (monthly average of 66.1%), while at 400 K the Sierra Madres and the Central United States combined constitute the dominant source region (monthly average of 44.1%, compared to 36.6% of the combined Intertropical Convergence Zone regions). When evaluating the impact of cross‐tropopause convection on the composition and chemistry of the upper troposphere and lower stratosphere, the effects of the NAMA on both the distribution of convective outflow and the residence time of convectively influenced air masses within the NAMA region must be considered., Key Points A trajectory analysis of overshooting tops identifies effect of North American Monsoon Anticyclone on cross‐tropopause convective outflowThe North American monsoons anticyclone's influence is greatest in August concurrent with the overshooting convection maximum frequencyThe intertropical convergence zone contributes most of the overshooting tops, but at upper levels other regions' contributions increase

Tropopause‐penetrating convection is a frequent seasonal feature of the Central United States climate. This convection presents the potential for consistent transport of water vapor into the upper troposphere and lower stratosphere (UTLS) through the lofting of ice, which then sublimates. Water vapor enhancements associated with convective ice lofting have been observed in both in situ and satellite measurements. These water vapor enhancements can increase the probability of sulfate aerosol‐catalyzed heterogeneous reactions that convert reservoir chlorine (HCl and ClONO2) to free radical chlorine (Cl and ClO) that leads to catalytic ozone loss. In addition to water vapor transport, lofted ice may also scavenge nitric acid and further impact the chlorine activation chemistry of the UTLS. We present a photochemical model that resolves the vertical chemical structure of the UTLS to explore the effect of water vapor enhancements and potential additional nitric acid removal. The model is used to define the response of stratospheric column ozone to the range of convective water vapor transported and the temperature variability of the lower stratosphere currently observed over the Central United States in conjunction with potential nitric acid removal and to scenarios of elevated sulfate aerosol surface area density representative of possible future volcanic eruptions or solar radiation management. We find that the effect of HNO3 removal is dependent on the magnitude of nitric acid removal and has the greatest potential to increase chlorine activation and ozone loss under UTLS conditions that weakly favor the chlorine activation heterogeneous reactions by reducing NOx sources., Key Points Photochemical box model defines the vertically resolved response of the stratosphere chemical composition to convective perturbationEffect of nitric acid removal on column ozone loss is dependent on favorability of initial conditions to heterogeneous chlorine activationNitric acid removal has the most impact on column ozone loss under conditions of mild favorability to chlorine activation

We analyzed the effect of the North American monsoon anticyclone (NAMA) on the meridional transport of summertime cross‐tropopause convective outflow by applying a trajectory analysis to a climatology of convective overshooting tops (OTs) identified in GOES satellite images, which covers the domain from 29°S to 68°N and from 205°W to 1.25°W for the time period of May to September, 2013. From this analysis, we identify seasonal development of geographically distinct outflow regions of convectively influenced air masses (CIAMs) from the NAMA circulation to the global stratosphere and quantify the associated meridional displacement of CIAMs. We find that prior to the development of the NAMA, the majority of CIAMs exit the study area in a southeastern region between 5°N and 35°N at 45°W (75.5% in May). During July and August, when the NAMA is strongest, two additional outflow regions develop that constitute the majority of outflow: 68.1% in a northeastern region between 35°N and 60°N at 45°W and 13.4% in a southwestern region between 5°N and 35°N at 145°W. The shift in the location of most CIAM outflow from the pre‐NAMA southeastern region to NAMA‐dependent northeastern and southwestern regions corresponds to a change in average meridional displacement of CIAMs from 3.3° northward in May to 24.5° northward in July and August. Meridional transport of CIAMs through persistent outflow regions from the NAMA circulation to the global stratosphere has the potential to impact global stratospheric composition beyond convective source regions., Key Points Trajectory analysis of overshooting tops identified by GOES satellite is used to evaluate meridional transport of cross‐tropopause convective outflowThe North American monsoon anticyclone (NAMA) circulation and its seasonality dictates the extent of meridional transport that occurs in the lower stratosphereDuring July and August, when the NAMA is strongest, the average convectively influenced air mass is transported 22.0° northward

Cerebellar plasticity is a critical mechanism for optimal feedback control. While Purkinje cell activity of the oculomotor vermis predicts eye movement speed and direction, more lateral areas of the cerebellum may play a role in more complex tasks, including decision-making. It is still under question how this motor-cognitive functional dichotomy between medial and lateral areas of the cerebellum plays a role in optimal feedback control. Here we show that elite athletes subjected to a trajectory prediction, go/no-go task manifest superior subsecond trajectory prediction accompanied by optimal eye movements and changes in cognitive load dynamics. Moreover, while interacting with the cerebral cortex, both the medial and lateral cerebellar networks are prominently activated during the fast feedback stage of the task, regardless of whether or not a motor response was required for the correct response. Our results show that cortico-cerebellar interactions are widespread during dynamic feedback and that experience can result in superior task-specific decision skills.

On August 27, 2013, during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) field mission, NASA's ER-2 research aircraft encountered a region of enhanced water vapor, extending over a depth of approximately 2 km and a minimum areal extent of 20,000 km2 in the stratosphere (375 K to 415 K potential temperature), south of the Great Lakes (42°N, 90°W). Water vapor mixing ratios in this plume, measured by the Harvard Water Vapor instrument, constitute the highest values recorded in situ at these potential temperatures and latitudes. An analysis of geostationary satellite imagery in combination with trajectory calculations links this water vapor enhancement to its source, a deep tropopause-penetrating convective storm system that developed over Minnesota 20 hours prior to the aircraft plume encounter. High resolution, ground-based radar data reveal that this system was comprised of multiple individual storms, each with convective turrets that extended to a maximum of ~4 km above the tropopause level for several hours. In situ water vapor data show that this storm system irreversibly delivered between 6.6 kt and 13.5 kt of water to the stratosphere. This constitutes a 20 – 25% increase in water vapor abundance in a column extending from 115 hP to 70 hPa over the plume area. Both in situ and satellite climatologies show a high frequency of localized water vapor enhancements over the central U.S. in summer, suggesting that deep convection can contribute to the stratospheric water budget over this region and season.

e18783 Background: Studies have suggested that pregnancy after breast cancer is safe, but the women who are able to conceive after cancer may also have a better prognosis. We sought to evaluate survival and obstetric outcomes among breast cancer patients in a population-based cohort. Methods: We studied women aged 18-45 years with a history of stage I-III breast cancer reported to the California Cancer Registry (CCR, 2000-2012). CCR data were linked to the 2000-2012 California Office of Statewide Health Planning and Development (OSHPD) birth cohort to ascertain both oncologic characteristics and obstetric outcomes. We compared overall survival (OS) for breast cancer patients who did or did not conceive at least 1 year after diagnosis. Breast cancer patients who conceived were matched in a 1:5 ratio to breast cancer patients who did not conceive via optimal bipartite matching accounting for follow-up time such that controls were diagnosed within a 3-month window of the cases and were alive at the time the case delivered; the distributions of cases and controls were directly balanced on socioeconomic and clinical covariates including stage, hormone receptors, and receipt of chemotherapy and radiation. For the obstetric outcomes, propensity score matching in a 1:5 ratio was used to match the same breast cancer patients who conceived to population based controls without cancer who delivered during the study years. Wald statistics, conditional Cox proportional hazards model, and conditional logistic regressions were used to evaluate outcomes. Results: We matched 417 patients aged 18-45 years at time of breast cancer diagnosis who conceived at least one year following diagnosis with 2,085 breast cancer patients who did not conceive. All covariates were balanced within 0.1 mean standardized difference. The majority of the cohort was non-Hispanic White (51%), with stage II disease (53%). The 5-year overall survival for cases relative to controls was 97.6% and 95.7% respectively. There was no difference in overall survival between patients who conceived and those who did not conceive following treatment for breast cancer (HR 0.58, 95% CI 0.3-1.1). Breast cancer patients did not have higher risks of preterm birth before 37 weeks (odds ratio [OR] 0.91, 95% CI 0.39-2.14), small-for-gestational age birthweight ( < 10th percentile: OR 0.93, 95% CI 0.67-1.29; < 5th percentile: OR 0.67, 95% CI 0.39-1.14), cesarean delivery (OR 1.12, 95% CI 0.92-1.35), severe maternal morbidity (OR 1.14, 95% CI 0.61-2.12), or neonatal morbidity (OR 1.08, 95% CI 0.77-1.53) relative to controls. Conclusions: In a population-based cohort, breast cancer patients who conceived at least 1 year after diagnosis did not have worse OS than matched breast cancer patients who did not conceive. Breast cancer patients who conceived during the study period did not have an increased risk of adverse obstetric outcomes compared to population-based controls without cancer.

Lumbar radicular pain is a significant burden for patients and is one of the most common complaints presented to spine practitioners. In the young, it is most often due to acute disc herniation, but in older patients, the onset is usually multifactorial. Most cases resolve on their own, but many patients experience recurrences. This chapter reviews a continuum of treatment options, from comprehensive physical rehabilitation to surgery. Understanding the pathophysiologic process may allow a more meaningful understanding of the development of chronic neuropathic pain of the extremity. A comprehensive history and physical examination, with findings confirmed by radiologic studies as warranted, may raise red flags early in the process and will facilitate efficient treatment of the underlying issues. An interdisciplinary approach may allow for earlier improvement and suitable treatment as needed.

We present the chain of mechanisms linking free radical catalytic loss of stratospheric ozone, specifically over the central United States in summer, to increased climate forcing by CO2 and CH4 from fossil fuel use. This case directly engages detailed knowledge, emerging from in situ aircraft observations over the polar regions in winter, defining the temperature and water vapor dependence of the kinetics of heterogeneous catalytic conversion of inorganic chlorine (HCl and ClONO2) to free radical form (ClO). Analysis is placed in the context of irreversible changes to specific subsystems of the climate, most notably coupled feedbacks that link rapid changes in the Arctic with the discovery that convective storms over the central US in summer both suppress temperatures and inject water vapor deep into the stratosphere. This places the lower stratosphere over the US in summer within the same photochemical catalytic domain as the lower stratosphere of the Arctic in winter engaging the risk of amplifying the rate limiting step in the ClO dimer catalytic mechanism by some six orders of magnitude. This transitions the catalytic loss rate of ozone in lower stratosphere over the United States in summer from HOx radical control to ClOx radical control, increasing the overall ozone loss rate by some two orders of magnitude over that of the unperturbed state. Thus we address, through a combination of observations and modeling, the mechanistic foundation defining why stratospheric ozone, vulnerable to increased climate forcing, is one of the most delicate aspects of habitability on the planet.

Many aspects of the complex relationship between working memory (WM) and long-term memory (LTM) remain unclear. Here, we manipulated task demands on a brief delayed-recognition paradigm to reveal behavioral and neural dissociations between these systems. Variations from a Baseline task included 3 challenges: increased delay duration, distraction during maintenance, and more closely matched memory probes, which were presented in behavioral experiments and during functional magnetic resonance imaging. Each of the challenges resulted in a significant decline in WM accuracy, and interestingly, a concurrent improvement in incidental LTM. Neural data revealed that, in task blocks, when participants anticipated, and then experienced, increased demands, they engaged medial temporal lobe (MTL) regions more during both the encoding and delay periods. Overall, these results indicate that distinct memory systems are recruited based on anticipated demands of a memory task, and MTL involvement underlies the observed dissociation between WM and LTM performance.

Johann Conrad Brunner (1653-1727) was a European anatomist and physician whose research concerning the pancreas and duodenum has made him a prominent figure in medicine. However, Brunner should also be recognized for his descriptions of syringomyelia, which were originally published in 1688 and included in the second edition of Theophilus Boneti's compendium of postmortem examinations, the Sepulchretum, which was published in 1700.Our current understanding of syringomyelia is based on the early observations of researchers such as Johann Conrad Brunner.

Long-term potentiation (LTP) is a synaptic mechanism underlying learning and memory that has been studied extensively in laboratory animals. The study of LTP recently has been extended into humans with repetitive sensory stimulation to induce cortical LTP. In this review article, we will discuss past results from our group demonstrating that repetitive sensory stimulation (visual or auditory) induces LTP within the sensory cortex (visual/auditory, respectively) and can be measured noninvasively with electroencephalography or functional magnetic resonance imaging. We will discuss a number of studies that indicate that this form of LTP shares several characteristics with the synaptic LTP described in animals: it is frequency dependent, long-lasting (> 1 hour), input-specific, depotentiates with low-frequency stimulation, and is blocked by N-methyl-D-aspartate receptor blockers in rats. In this review, we also present new data with regard to the behavioral significance of human sensory LTP. These advances will permit enquiry into the functional significance of LTP that has been hindered by the absence of a human model. The ability to elicit LTP with a natural sensory stimulus noninvasively will provide a model system allowing the detailed examination of synaptic plasticity in normal subjects and might have future clinical applications in the diagnosis and assessment of neuropsychiatric and neurocognitive disorders.

Elite sports performance fundamentally relies on a complex set of brain functions engaged once visual signals are relayed from the eye. In this review, we overview a series of these neural mechanisms-focusing specifically on the critical role of attention in sculpting the visual processing that takes place leading up to a decision. These brain functions are introduced within the theoretical concept of the 'Perception-Action Cycle.' Vision does not stop at the eye but requires a coordinated set of brain mechanisms called on to convert visual input into rapid decisions about action.

Multitasking negatively influences the retention of information over brief periods of time. This impact of interference on working memory is exacerbated with normal aging. We used functional MRI to investigate the neural basis by which an interruption is more disruptive to working memory performance in older individuals. Younger and older adults engaged in delayed recognition tasks both with and without interruption by a secondary task. Behavioral analysis revealed that working memory performance was more impaired by interruptions in older compared with younger adults. Functional connectivity analyses showed that when interrupted, older adults disengaged from a memory maintenance network and reallocated attentional resources toward the interrupting stimulus in a manner consistent with younger adults. However, unlike younger individuals, older adults failed to both disengage from the interruption and reestablish functional connections associated with the disrupted memory network. These results suggest that multitasking leads to more significant working memory disruption in older adults because of an interruption recovery failure, manifest as a deficient ability to dynamically switch between functional brain networks.

Our ability to focus attention on task-relevant stimuli and ignore irrelevant distractions is reflected by differential enhancement and suppression of neural activity in sensory cortices. Previous research has shown that older adults exhibit a deficit in suppressing task-irrelevant information, the magnitude of which is associated with a decline in working memory performance. However, it remains unclear if a failure to suppress is a reflection of an inability of older adults to rapidly assess the relevance of information upon stimulus presentation when they are not aware of the relevance beforehand. To address this, we recorded the electroencephalogram (EEG) in healthy older participants (aged 60—80 years) while they performed two different versions of a selective face/scene working memory task, both with and without prior knowledge as to when relevant and irrelevant stimuli would appear. Each trial contained two faces and two scenes presented sequentially followed by a 9 sec delay and a probe stimulus. Participants were given the following instructions: remember faces (ignore scenes), remember scenes (ignore faces), remember the xth and yth stimuli (where x and y could be 1st, 2nd, 3rd or 4th), or passively view all stimuli. Working memory performance remained consistent regardless of task instructions. Enhanced neural activity was observed at posterior electrodes to attended stimuli, while neural responses that reflected the suppression of irrelevant stimuli was absent for both tasks. The lack of significant suppression at early stages of visual processing was revealed by P1 amplitude and N1 latency modulation indices. These results reveal that prior knowledge of stimulus relevance does not modify early neural processing during stimulus encoding and does not improve working memory performance in older adults. These results suggest that the inability to suppress irrelevant information early in the visual processing stream by older adults is related to mechanisms specific to top-down suppression.

The inhalation toxicology studies available in the public domain have been reviewed to establish a database for inhalation toxicology and derive thresholds of toxicological concern (TTC) for effects in the respiratory tract and systemically for Cramer class 1 and 3 chemicals. These TTCs can be used as the basis for developing an exposure based waiving (EBW) approach to evaluating the potential for adverse effects from exposure to ingredients in aerosol products, used by consumers. The measurement of consumer exposure in simulated product use is key to the application of an exposure based waiving approach to evaluating potential consumer risk. The detailed exposure evaluation for aerosol ingredients with defined use scenarios, in conjunction with an evaluation of the potential structure activity relationship for toxicity and the TTCs for inhalation exposure could be used to waive undertaking inhalation toxicology studies under REACH. Not all classes of chemicals are suitable for such an approach, but for chemicals with a predictable low potential toxicity, and very low levels of exposure, this approach, could reduce the amount of inhalation toxicology studies required for the implementation of the European REACH legislation. Such an approach is consistent with the concept of developing 'intelligent testing strategies' for REACH.

Long-term potentiation (LTP) is the principal candidate synaptic mechanism underlying learning and memory, and has been studied extensively at the cellular and molecular level in laboratory animals. Inquiry into the functional significance of LTP has been hindered by the absence of a human model as, until recently, LTP has only been directly demonstrated in humans in isolated cortical tissue obtained from patients undergoing surgery, where it displays properties identical to those seen in non-human preparations. In this brief review, we describe the results of paradigms recently developed in our laboratory for inducing LTP-like changes in visual-, and auditory-evoked potentials. We describe how rapid, repetitive presentation of sensory stimuli leads to a persistent enhancement of components of sensory-evoked potential in normal humans. Experiments to date, investigating the locus, stimulus specificity, and NMDA receptor dependence of these LTP-like changes suggest that they have the essential characteristics of LTP seen in experimental animals. The ability to elicit LTP from non-surgical patients will provide a human model system allowing the detailed examination of synaptic plasticity in normal subjects and may have future clinical applications in the assessment of cognitive disorders. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

It had been shown previously that a photic tetanus induces LTP-like changes in the visual cortex, as indexed by an enhancement of the N1b component of the visual evoked potential, recorded non-invasively by electroencephalography. This potentiation was shown to last over 1 h. In the present study, the effect of a photic tetanus on oscillatory activity is investigated. EEGs were collected from eight healthy subjects in three conditions while visual checkerboards were displayed. Following baseline presentations in two conditions a lateralized visual tetanus was given, either to the left or right visual field, and in a third condition no tetanus was given. This was followed by a return to baseline presentations, both immediately after the tetanus/control block, and 1 h later. Enhanced event-related desynchronization (ERD) of the alpha rhythm lasting 1 h was seen following the photic tetanus over occipital electrodes. Because ERD of the alpha rhythm is thought to represent active cortex, these results suggest that the visual tetanus induces long-lasting cortical changes, with stronger neuronal assemblies and increased neuronal output.

Applying functional magnetic resonance imaging techniques, hemodynamic responses elicited by slowly flashing checkerboards (0.25 Hz) were measured both before and after a block of rapidly presented checkerboards (9 Hz -- a 'photic tetanus') was delivered. It has been shown previously, using electroencephalography, that this photic tetanus potentiates components of the visual-evoked potential. In the present study, hemodynamic responses in the extrastriate visual cortex were significantly increased to checkerboards presented at a low frequency after the administration of the photic tetanus. These results support the idea that long-term potentiation can be demonstrated non-invasively within the human visual cortex and provide evidence that the plastic changes are localized within the secondary visual cortex.

High-frequency, repetitive, auditory stimulation was used to determine whether induction of a long-lasting increase of the human auditory evoked potential (AEP) was possible. Recording non-invasively with electroencephalogram scalp electrodes, stable increases in amplitude were observed in the N1 component of the AEP, which is thought to reflect activity within auditory cortex (N1). The increase was maintained over an hour and was shown to be independent of alterations in the state of arousal. This is the first demonstration of the induction of long-lasting plastic changes in AEPs, and suggest that this represents the first direct demonstration of long-term potentiation in the auditory cortex of normal, intact humans.

The effects of various lattice defects, such as a single edge dislocation, dislocation configurations, a low-angle grain boundary, and a high-angle grain boundary, on martensite nucleation and growth were investigated by performing molecular dynamics simulations, using EAM interatomic potentials for Ni-Al alloy. Stress induced and thermally activated martensitic transformations were studied in the cases that various defects were introduced into the simulated system. The simulation results show that the nucleation patterns were closely related to the stresses of the dislocation configurations, in the sense that the locations where stresses assist the lattice distortion of the transformation are favorable for martensite nucleation. A symmetric, tilt low-angle grain boundary is not favorable for martensite nucleation, because the stresses of the constituent dislocations cancel one another and stresses that assist the lattice distortion cannot be produced. The low-angle boundary hinders the martensite growth due to the high stability of this type of dislocation configuration. A relaxed, high-angle grain boundary (coincident site lattice) is also not favorable for martensite nucleation, because of the lack of long-range stress field. (C) 2004 American Institute of Physics.

Objective : We measured late cortical potentials in a psychophysical procedure for binaural unmasking of a dichotically-embedded pitch. Methods : Late-latency auditory evoked potentials were measured from 128 recording channels in 13 healthy subjects. Control stimuli consisted of 500 ms segments of broadband acoustic noise presented identically to both ears via earphones, evoking a perception of noise localized in the centre of the head. Dichotic pitch stimuli were created by introducing a dichotic delay to a narrow frequency region of the same noise segments, and resulted in a perception of both the centrally-located noise and a right-lateralized pitch. Results : Both stimuli evoked late auditory event-related potentials (ERPs) characterized by a P1-N1-P2 complex of waves between 60 and 180 ms after stimulus onset. ERPs associated with the control and dichotic pitch stimuli showed no amplitude differences for the P1 and N1 waves. ERPs to dichotic pitch stimuli became significantly more negative beginning at a latency around 150 ms, an effect that was maximal between 210 and 280 ms. Topographic mapping showed that this late negativity was lateralized to the left hemisphere. Conclusions : The late negative wave elicited by the dichotic pitch stimulus reflects neural processing that is dependent upon binaural fusion within the auditory system. Significance : The dichotic pitch paradigm may provide a useful tool for the electrophysiological assessment and study of the temporal processing capabilities of the auditory system. This paradigm may also be useful for the study of binaural mechanisms for the perceptual segregation of concurrent sound sources.

A novel method of calculation of heat dissipation during sliding between metals was presented by using molecular dynamics. Temperature distribution in the regions near the contact interface was calculated. The calculation results show that plastic deformation in the near-surface regions accounts for most of the friction heat and the temperature increase. Friction heat was built up in the regions subject to plastic deformation. In the case that no plastic deformation occurred, elastic waves contributed mainly to the energy dissipation so that no large heat buildup could take place in the vicinity of the contact regions. (C) 2002 Elsevier Science Ltd. All rights reserved.

Molecular dynamics simulation was carried out to investigate the stick-slip on an atomic scale by using the embedded atom method potential for Ni–Al. The analyses of the dynamic features of the atoms in the sliding block clearly show that the elastic deformation of the surface layers is the main cause for the stick-slip phenomenon, which is consistent with the macroscopic stick-slip. The simulation results also indicate that phonons are emitted during stick-slip, and a commensurate fit between the contacting surfaces is not significant for the stick-slip friction.

We report on the transport properties of ABC and ABA stacked trilayer graphene using dual, locally gated field effect devices. The high efficiency and large breakdown voltage of the HfO2 top and bottom gates enables independent tuning of the perpendicular electric field and the Fermi level over an unprecedentedly large range. We observe a resistance change of six orders of magnitude in the ABC trilayer, which demonstrates the opening of a band gap. Our data suggest that the gap saturates at a large displacement field of D ~ 3 V/nm, in agreement with self-consistent Hartree calculations. In contrast, the ABA trilayer remains metallic even under a large perpendicular electric field. Despite the absence of a band gap, the band structure of the ABA trilayer continues to evolve with increasing D. We observe signatures of two-band conduction at large D fields. Our self-consistent Hartree calculation reproduces many aspects of the experimental data, but also points to the need for more sophisticated theory.

During the fifth flight of the Microwave Anisotropy Experiment (MAX5), we revisited a region with significant dust emission near the star Mu Pegasi. A 3.5 cm$^{-1}$ low frequency channel has been added since the previous measurement (\cite{mei93a}). The data in each channel clearly show structure correlated with IRAS 100 \micron\ dust emission. The spectrum of the structure in the 6, 9 and 14 cm$^{-1}$ channels is described by $I_{\nu}\propto\nu^{\beta}B_{\nu}(T_{dust})$, where $\beta$ = 1.3 and $T_{dust}$ = 19~K and $B_{\nu}$ is the Planck function. However, this model predicts a smaller amplitude in the 3.5 cm$^{-1}$ band than is observed. Considering only linear combinations of the data independent of the best fit foreground spectrum for the three lower channels, we find an upper limit to CMBR fluctuations of $\Delta T/T = \langle \frac{C_l~l(l+1)}{2\pi}\rangle^{\frac{1}{2}} \leq 1.3\times 10^{-5}$ at the 95\% confidence level. The result is for a flat band power spectrum and does not include a 10\% uncertainty in calibration. It is consistent with our previous observation in the region.

Both thermally induced and stress-induced coherent nucleation and growth of an L10 martensitic phase have been examined and analyzed at the atomic level in molecular dynamics (MD) computer simulations of an ordered B2 NiAl lattice array using embedded atom method (EAM) interatomic potentials. Both heterogeneous and homogeneous nucleation are observed, the latter requiring an applied stress. The heterogeneous process occurs at ledge corners on stepped free surfaces and can be analyzed in terms of localized soft modes. The homogeneous nucleation can be understood as resulting from a strain spinodal instability which produces a morphology reminiscent of chemical spinodal decomposition. Self-accommodating martensite variants appear very early in the growth process, and all interfaces remain coherent with no detectable presence of dislocations in these early stages.

The microscopic mechanism of 'transformation toughening' is thought to be the stress reduction at a crack tip resulting from a displacive phase transformation induced by the stress field of a crack under external loading. Whether transformation toughening or 'transformation embrittlement' is the result depends on many different characteristics of the displacive transformation, as well as the geometry of the stress field of the crack. Since both crack and displacive transformation dynamics are sufficiently rapid to be suitably simulated in a molecular dynamics scheme we have explored this approach with the ordered intermetallic NiAl, employing embedded atom method (EAM) potentials. These potentials, in turn, have allowed the construction of a Ginzburg-Landau strain free energy functional (with all the material dependent parameters determined from molecular dynamics simulations), which may then be used to carry out Monte Carlo simulations of the crack-transformation zone interaction on a substantially larger spatial scale. These various types of simulation will be described and the results analysed.

Using molecular dynamics computer simulations and interatomic potentials derived partly by Voter and Chen1 and Rifkin et al.,2 we studied the surface reconstruction taking place on free surfaces of arrays of RuAl. Surface reconstruction appears to be very important on {111} and {110} types of planes and almost nonexistent on {100} type of planes. Cracks oriented so that their crack planes were either {111} types or {110} types exhibit on their internal free surface important surface reconstruction. It is believed that this effect may have some contribution in the brittle versus ductile behavior of the crack.

The balloon-borne Millimeter-Wave Anisotropy Experiment (MAX) is designed to measure the fluctuations in the cosmic microwave background (CMB) on angular scales from 0.3 to several degrees. The long term goal is to measure many pixels on the sky at a level approaching ΔT/T(CMB) = 1 × 10−6. These angular scales fill an important gap between the angular scales ⩽10arcmin which are accessible from conventional radio telescopes and the angular scales ⩾ 7 deg which have been measured by the COBE satellite. They are of particular importance to scientific issues such as galaxy formation, dark matter, and the Sunyaev-Zel'dovich effect.

Background Impaired cortical plasticity may be part of the core pathophysiology of schizophrenia (SZ). Long-term potentiation is a form of neuroplasticity that has been recently demonstrated in humans by showing that repetitive visual stimulation produces lasting enhancement of visual evoked potentials (VEP). Using this paradigm, we examined whether visual cortical plasticity is impaired in SZ. Methods Electroencephalographic data were recorded from 19 SZ and 22 healthy control (HC) subjects during a visual long-term potentiation paradigm. Visual evoked potentials were elicited by standard visual stimuli (∼.83 Hz, 2-minute blocks) at baseline and at 2, 4, and 20 minutes following exposure to visual high-frequency stimulation (HFS) (∼8.8 Hz, 2 minutes) designed to induce VEP potentiation. To ensure attentiveness during VEP assessments, subjects responded with a button press to infrequent (10%) target stimuli. Visual evoked potentials were subjected to principal components analysis. Two negative-voltage components prominent over occipital-parietal electrode sites were evident at 92 msec (C1) and at 146 msec (N1b). Changes in C1 and N1b component scores from baseline to the post-HFS assessments were compared between groups. Results High-frequency stimulation produced sustained potentiation of visual C1 and N1b in HCs but not in SZs. The HCs and SZs had comparable HFS-driven electroencephalographic visual steady state responses. However, greater visual steady state responses to the HFS predicted greater N1b potentiation in HCs but not in SZs. Schizophrenia patients with greater N1b potentiation decreased their reaction times to target stimuli. Conclusions Visual cortical plasticity is impaired in schizophrenia, consistent with hypothesized deficits in N -methyl-D-aspartate receptor function.

Molecular dynamics simulations of fracture have been performed on the metals Al and Nb, and the intermetallic alloys RuAl, Nb 3 Al and NiAl. The forces and energies were modelled with embedded atom method potentials. The increasing external stress was applied using displacements of the outer boundaries of the array, calculated by anisotropic elasticity theory, until the pre-existing cracks propagated or dislocation nucleation occurred. The resulting critical stress intensity factor was calculated at various orientations and temperatures, and the results compared with theory. Observations of slip systems are reported, as well as values for surface energies and “unstable stacking” energies.

Using Molecular Dynamics and an Embedded Atom Method (EAM) potential derived by Voter and Chen [1] for the NiAl binary alloy system, simulations of the crystalline to amorphous transition have been performed in fcc Al and L12 Ni3Al lattices containing approximately 10 000 atoms under shock loading conditions. With tensile stress simulations, at 300 K Al turned amorphous after copious emission of dislocations, while at 10 K it did not become amorphous. The regions of amorphisation were found to be well correlated to high levels of local volume change (ΔV/V = 10%). For the Ni3Al simulations, only shear stresses were used, and in this case the onset of amorphisation appeared to be triggered by copious dislocation multiplication. Both homogeneous and heterogeneous nucleations were observed and the propagation pattern of the amorphisation transformation very much resembled a percolation process.

An exact nucleation energy formula has been derived for the fluctuation energy necessary to initiate a coherent martensitic transformation in the strain field of a defect of arbitrary potency within the framework of a standard Ginzburg-Landau strain free energy model of the form: f(η) = g(η) + K 1 (▿η) 2 . The formula is limited to planar defects and planar interface propagation geometries, and precursor metastable strain profiles are calculated exactly. The defect induced strain field expands as the driving force is increased until the athermal instability limit is reached. This limit can be simply expressed in terms of the defect potency, or alternatively in terms of the strain spinodal, but the latter condition proves to be the weaker of the two in most cases tested. Once the nucleation condition is achieved, the equations of growth become identical to those previously derived by Chan. Some considerations are also given to the extended free energy form: f(η) = g(η) + K 1 (▿η) 2 + K 2 (▿ 2 η) 2 where it is found that for some values of K 2 and K 1 , a defect will be decorated by an oscillatory strain field, in others a monotonically decaying field, and in a third range, no metastable defect strain field appears to be possible at all.

Resorbable subcuticular staples are a new way to close surgical wounds and have not been reported in the orthopedic literature. This randomized, controlled study compared a resorbable subcuticular staple system with stainless steel wound stapling in patients undergoing unilateral primary total hip arthroplasty (THA). Institutional Review Board approval and patient consent was obtained for all patients. Sixty patients (30 each group) were randomized to receive either resorbable subcuticular staples or stainless steel staples after primary THA. Incision length, number of staples used, and any staple insertion problems were recorded. Subjective reports of pain levels or incision complaints were solicited, and wound photographs were obtained on days 1 and 14 and 6 weeks postoperatively. The presence of wound drainage, erythema, wound separation, or echymosis was recorded at each visit, as well as all postoperative complications. The average incision length in the resorbable group was 13.2 cm and required 16 staples for closure, compared to 15 cm and 20 staples for the metal staple group. No infections occurred in either group, although the incidence of erythema and wound drainage at 2 weeks was higher for patients in the stainless steel group. One patient with metal staples had a postoperative hematoma requiring secondary irrigation and debridement. Patient satisfaction was higher with the resorbable staples. A resorbable subcuticular staple system can provide comparable wound closure to stainless steel staples following THA and may do so with less local discomfort, wound drainage, or erythematous reaction.

Selective attention confers a behavioral benefit on both perceptual and working memory (WM) performance, often attributed to top–down modulation of sensory neural processing. However, the direct relationship between early activity modulation in sensory cortices during selective encoding and subsequent WM performance has not been established. To explore the influence of selective attention on WM recognition, we used electroencephalography to study the temporal dynamics of top–down modulation in a selective, delayed-recognition paradigm. Participants were presented with overlapped, “double-exposed” images of faces and natural scenes, and were instructed to either remember the face or the scene while simultaneously ignoring the other stimulus. Here, we present evidence that the degree to which participants modulate the early P100 (97–129 msec) event-related potential during selective stimulus encoding significantly correlates with their subsequent WM recognition. These results contribute to our evolving understanding of the mechanistic overlap between attention and memory.

Interference is known to negatively impact the ability to maintain information in working memory (WM), an effect that is exacerbated with aging. Here, we explore how distinct sources of interference, i.e., distraction (stimuli to-be-ignored) and interruption (stimuli requiring attention), differentially influence WM in younger and older adults. EEG was recorded while participants engaged in three versions of a delayed-recognition task: no interference, a distracting stimulus, and an interrupting stimulus presented during WM maintenance. Behaviorally, both types of interference negatively impacted WM accuracy in older adults significantly more than younger adults (with a larger deficit for interruptions). N170 latency measures revealed that the degree of processing both distractors and interruptors predicted WM accuracy in both populations. However, while WM impairments could be explained by excessive attention to distractors by older adults (a suppression deficit), impairment induced by interruption were not clearly mediated by age-related increases in attention to interruptors. These results suggest that distinct underlying mechanisms mediate the impact of different types of external interference on WM in normal aging.

Normal aging is associated with a degradation of perceptual abilities and a decline in higher-level cognitive functions, notably working memory. To remediate age-related deficits, cognitive training programs are increasingly being developed. However, it is not yet definitively established if, and by what mechanisms, training ameliorates effects of cognitive aging. Furthermore, a major factor impeding the success of training programs is a frequent failure of training to transfer benefits to untrained abilities. Here, we offer the first evidence of direct transfer-of-benefits from perceptual discrimination training to working memory performance in older adults. Moreover, using electroencephalography to evaluate participants before and after training, we reveal neural evidence of functional plasticity in older adult brains, such that training-induced modifications in early visual processing during stimulus encoding predict working memory accuracy improvements. These findings demonstrate the strength of the perceptual discrimination training approach by offering clear psychophysical evidence of transfer-of-benefit and a neural mechanism underlying cognitive improvement.

The negative impact of external interference on working memory (WM) performance is well documented; yet, the mechanisms underlying this disruption are not sufficiently understood. In this study, electroencephalogram and functional magnetic resonance imaging (fMRI) data were recorded in separate experiments that each introduced different types of visual interference during a period of WM maintenance: distraction (irrelevant stimuli) and interruption (stimuli that required attention). The data converged to reveal that regardless of the type of interference, the magnitude of processing interfering stimuli in the visual cortex (as rapidly as 100 ms) predicted subsequent WM recognition accuracy for stored items. fMRI connectivity analyses suggested that in the presence of distraction, encoded items were maintained throughout the delay period via connectivity between the middle frontal gyrus and visual association cortex, whereas memoranda were not maintained when subjects were interrupted but rather reactivated in the postinterruption period. These results elucidate the mechanisms of external interference on WM performance and highlight similarities and differences of distraction and multitasking.