Bond-forming reactions of N22+ with C2H4, C2H6, C3H4 and C3H6

Mass spectrometry, coupled with position-sensitive coincidence detection, has been used to investigate the reactions of N22+ with various small hydrocarbon molecules (C2H4, C2H6, C3H4, c-C3H6 and n-C3H6) at collision energies below 10 eV in the centre-of-mass frame. The reactivity, in each case, is dominated by electron transfer. However, in each collision system we also clearly identify products formed following the creation of new chemical bonds. These bond-forming reactions comprise two distinct classes: (i) hydride transfer reactions which initially form NnH+ (n = 1, 2) and (ii) N+ transfer reactions which form monocationic products with Csingle bondN bonds. These bond-forming reactions make a small (5–10%), but significant, contribution to the overall product ion yield in each collision system. The temporal and positional data recorded by our coincidence detection technique are used to construct scattering diagrams which reveal the mechanisms of the bond-forming reactions. For the hydride transfer process, the scattering diagrams reveal that H− is directly transferred from the hydrocarbon to N22+ at significant interspecies separations. For the hydride transfer reactions with C2H4, C2H6 and C3H4, we observe fragmentation of the nascent N2H+* to form NH+ + N. The N+ transfer reaction also proceeds by a direct mechanism: a single step involving N+/H exchange results in the formation of a singly-charged organic species containing a Csingle bondN bond which is detected in coincidence with H+. The two general classes of bond-forming reactivity we observe in the reactions of N22+ with organic molecules may be relevant in the chemistry of energised environments rich in molecular nitrogen and hydrocarbon species, such as the atmosphere of Titan

Two cases of food aversion with semantic dementia

Accounts of altered eating behavior in semantic dementia generally emphasize gluttony and abnormal food preferences. Here we describe two female patients with no past history of eating disorders who developed early prominent aversion to food in the context of an otherwise typical semantic dementia syndrome. One patient (aged 57) presented features in line with anorexia nervosa while the second patient (aged 58) presented with a syndrome more suggestive of bulimia nervosa. These cases add to the growing spectrum of apparently dichotomous behavior patterns in the frontotemporal dementias and illustrate a potentially under-recognized cause of eating disorders presenting in later life

Compulsive versifying after treatment of transient epileptic amnesia

Compulsive production of verse is an unusual form of hypergraphia that has been reported mainly in patients with right temporal lobe seizures. We present a patient with transient epileptic amnesia and a left temporal seizure focus, who developed isolated compulsive versifying, producing multiple rhyming poems, following seizure cessation induced by lamotrigine. Functional neuroimaging studies in the healthy brain implicate left frontotemporal areas in generating novel verbal output and rhyme, while dysregulation of neocortical and limbic regions occurs in temporal lobe epilepsy. This case complements previous observations of emergence of altered behavior with reduced seizure frequency in patients with temporal lobe epilepsy. Such cases suggest that reduced seizure frequency has the potential not only to stabilize or improve memory function, but also to trigger complex, specific behavioral alterations

Electron transfer and bond-forming reactions following collisions of I2+ with CO and CS2

Collisions between I2+ and CO have been investigated using time-of flight mass spectrometry at a range of centre-of-mass collision energies between 0.5 eV and 3.0 eV. Following I2+ + CO collisions we detect I+ + CO+ from a single-electron transfer reaction and IO+ + C+ from bond-forming reactivity. Reaction-window calculations, based on Landau-Zener theory, have been used to rationalise the electron transfer reactivity and computational chemistry has been used to explore the [I-CO] 2+ potential energy surface to account for the observation of IO+. In addition, collisions between I2+ and CS2 have been investigated over a range of centre-of-mass collision energies between 0.8 eV and 6.0 eV. Both single and double electron transfer reactions are observed in the I2+/CS2 collision system, an observation again rationalized by reaction-window theory. The monocations IS+ and IC+ are also detected following collisions of I2+ with CS2, and these ions are clearly products from a bond-forming reaction. We present a simple model based on the structure of the [I-CS2]2+ collision complex to rationalize the significantly larger yield of IS+ than IC+ in this bond-forming process

Who Watches the Watchmen? An Appraisal of Benchmarks for Multiple Sequence Alignment

Multiple sequence alignment (MSA) is a fundamental and ubiquitous technique in bioinformatics used to infer related residues among biological sequences. Thus alignment accuracy is crucial to a vast range of analyses, often in ways difficult to assess in those analyses. To compare the performance of different aligners and help detect systematic errors in alignments, a number of benchmarking strategies have been pursued. Here we present an overview of the main strategies--based on simulation, consistency, protein structure, and phylogeny--and discuss their different advantages and associated risks. We outline a set of desirable characteristics for effective benchmarking, and evaluate each strategy in light of them. We conclude that there is currently no universally applicable means of benchmarking MSA, and that developers and users of alignment tools should base their choice of benchmark depending on the context of application--with a keen awareness of the assumptions underlying each benchmarking strategy.Comment: Revie

A physiological signature of sound meaning in dementia.

The meaning of sensory objects is often behaviourally and biologically salient and decoding of semantic salience is potentially vulnerable in dementia. However, it remains unclear how sensory semantic processing is linked to physiological mechanisms for coding object salience and how that linkage is affected by neurodegenerative diseases. Here we addressed this issue using the paradigm of complex sounds. We used pupillometry to compare physiological responses to real versus synthetic nonverbal sounds in patients with canonical dementia syndromes (behavioural variant frontotemporal dementia - bvFTD, semantic dementia - SD; progressive nonfluent aphasia - PNFA; typical Alzheimer's disease - AD) relative to healthy older individuals. Nonverbal auditory semantic competence was assessed using a novel within-modality sound classification task and neuroanatomical associations of pupillary responses were assessed using voxel-based morphometry (VBM) of patients' brain MR images. After taking affective stimulus factors into account, patients with SD and AD showed significantly increased pupil responses to real versus synthetic sounds relative to healthy controls. The bvFTD, SD and AD groups had a nonverbal auditory semantic deficit relative to healthy controls and nonverbal auditory semantic performance was inversely correlated with the magnitude of the enhanced pupil response to real versus synthetic sounds across the patient cohort. A region of interest analysis demonstrated neuroanatomical associations of overall pupil reactivity and differential pupil reactivity to sound semantic content in superior colliculus and left anterior temporal cortex respectively. Our findings suggest that autonomic coding of auditory semantic ambiguity in the setting of a damaged semantic system may constitute a novel physiological signature of neurodegenerative diseases

Thermal-Error Regime in High-Accuracy Gigahertz Single-Electron Pumping

Single-electron pumps based on semiconductor quantum dots are promising candidates for the emerging quantum standard of electrical current. They can transfer discrete charges with part-per-million (ppm) precision in nanosecond time scales. Here, we employ a metal-oxide-semiconductor silicon quantum dot to experimentally demonstrate high-accuracy gigahertz single-electron pumping in the regime where the number of electrons trapped in the dot is determined by the thermal distribution in the reservoir leads. In a measurement with traceability to primary voltage and resistance standards, the averaged pump current over the quantized plateau, driven by a 1-GHz sinusoidal wave in the absence of a magnetic field, is equal to the ideal value of ef within a measurement uncertainty as low as 0.27 ppm

Agnosia for accents in primary progressive aphasia.

As an example of complex auditory signal processing, the analysis of accented speech is potentially vulnerable in the progressive aphasias. However, the brain basis of accent processing and the effects of neurodegenerative disease on this processing are not well understood. Here we undertook a detailed neuropsychological study of a patient, AA with progressive nonfluent aphasia, in whom agnosia for accents was a prominent clinical feature. We designed a battery to assess AA's ability to process accents in relation to other complex auditory signals. AA's performance was compared with a cohort of 12 healthy age and gender matched control participants and with a second patient, PA, who had semantic dementia with phonagnosia and prosopagnosia but no reported difficulties with accent processing. Relative to healthy controls, the patients showed distinct profiles of accent agnosia. AA showed markedly impaired ability to distinguish change in an individual's accent despite being able to discriminate phonemes and voices (apperceptive accent agnosia); and in addition, a severe deficit of accent identification. In contrast, PA was able to perceive changes in accents, phonemes and voices normally, but showed a relatively mild deficit of accent identification (associative accent agnosia). Both patients showed deficits of voice and environmental sound identification, however PA showed an additional deficit of face identification whereas AA was able to identify (though not name) faces normally. These profiles suggest that AA has conjoint (or interacting) deficits involving both apperceptive and semantic processing of accents, while PA has a primary semantic (associative) deficit affecting accents along with other kinds of auditory objects and extending beyond the auditory modality. Brain MRI revealed left peri-Sylvian atrophy in case AA and relatively focal asymmetric (predominantly right sided) temporal lobe atrophy in case PA. These cases provide further evidence for the fractionation of brain mechanisms for complex sound analysis, and for the stratification of progressive aphasia syndromes according to the signature of nonverbal auditory deficits they produce

The brain basis of musicophilia: evidence from frontotemporal lobar degeneration.

Musicophilia, or abnormal craving for music, is a poorly understood phenomenon that has been associated in particular with focal degeneration of the temporal lobes. Here we addressed the brain basis of musicophilia using voxel-based morphometry (VBM) on MR volumetric brain images in a retrospectively ascertained cohort of patients meeting clinical consensus criteria for frontotemporal lobar degeneration: of 37 cases ascertained, 12 had musicophilia, and 25 did not exhibit the phenomenon. The syndrome of semantic dementia was relatively over-represented among the musicophilic subgroup. A VBM analysis revealed significantly increased regional gray matter volume in left posterior hippocampus in the musicophilic subgroup relative to the non-musicophilic group (p < 0.05 corrected for regional comparisons); at a relaxed significance threshold (p < 0.001 uncorrected across the brain volume) musicophilia was associated with additional relative sparing of regional gray matter in other temporal lobe and prefrontal areas and atrophy of gray matter in posterior parietal and orbitofrontal areas. The present findings suggest a candidate brain substrate for musicophilia as a signature of distributed network damage that may reflect a shift of hedonic processing toward more abstract (non-social) stimuli, with some specificity for particular neurodegenerative pathologies