169 research outputs found
Carbon nanotube junctions and devices
No full textIn this thesis Postma presents transport experiments performed on individual single-wall carbon nanotubes. Carbon nanotubes are molecules entirely made of carbon atoms. The electronic properties are determined by the exact symmetry of the nanotube lattice, resulting in either metallic or semiconducting behaviour. Due to their small diameter, electronic motion is directed in the length direction of the nanotube, making them ideal systems to study e.g. one-dimensional transport phenomena. First, we present mK-temperature current-voltage characteristics of an individual single-wall carbon nanotube showing Coulomb blockade and resonant tunnelling through individual molecular levels. We then report electrical transport measurements on carbon nanotubes with naturally occurring intramolecular junctions. We find that a metal-semiconductor junction behaves like a rectifying diode, whereas the conductance of a metal-metal junction behaves like a tunnel junction with associated power-law dependencies described by a Luttinger liquid model for tunnelling between the two nanotube segments. In order to further study carbon nanotube intramolecular junctions, we developed an atomic force microscope (AFM) manipulation technique, by means of which carbon nanotube junctions such as buckles and crossings are created. The electronic transport properties of these manipulated structures show that they form electronic nanometer-size tunnel junctions. Thereafter, room-temperature single-electron transistors are realized within metallic carbon nanotubes. The devices feature a short (down to 20 nm) nanotube section that is created by AFM manipulation. Coulomb charging is observed at room temperature. We observe unconventional power-law dependencies in the transport properties for which we develop a resonant-tunnelling Luttinger-liquid model. Finally, the low-frequency electronic noise properties of metallic carbon nanotubes are investigated. The noise power exhibits a 1/f frequency dependence that is three orders of magnitude smaller at 8 K than at 300 K. As a demonstration of how these noise properties affect nanotube devices, we present a preliminary investigation of the noise characteristics of an intramolecular carbon nanotube single-electron transistor.Applied Science
Neutron diffractometer INES for quantitative phase analysis of archaeological objects
No full textApplied Science
Improved analysis of parity violation at neutron p-wave resonances of 238U based on resonance spin assignments
No full textDependence of the populations of low-energy levels in 108,110Ag on the resonance spin and parity
No full text
Lack of multisensory integration in hemianopia: no influence of visual stimuli on aurally guided saccades to the blind hemifield
No full textIn patients with visual hemifield defects residual visual functions may be present, a phenomenon called blindsight. The superior colliculus (SC) is part of the spared pathway that is considered to be responsible for this phenomenon. Given that the SC processes input from different modalities and is involved in the programming of saccadic eye movements, the aim of the present study was to examine whether multimodal integration can modulate oculomotor competition in the damaged hemifield. We conducted two experiments with eight patients who had visual field defects due to lesions that affected the retinogeniculate pathway but spared the retinotectal direct SC pathway. They had to make saccades to an auditory target that was presented alone or in combination with a visual stimulus. The visual stimulus could either be spatially coincident with the auditory target (possibly enhancing the auditory target signal), or spatially disparate to the auditory target (possibly competing with the auditory tar-get signal). For each patient we compared the saccade endpoint deviation in these two bi-modal conditions with the endpoint deviation in the unimodal condition (auditory target alone). In all seven hemianopic patients, saccade accuracy was affected only by visual stimuli in the intact, but not in the blind visual field. In one patient with a more limited quadrantano-pia, a facilitation effect of the spatially coincident visual stimulus was observed. We conclude that our results show that multisensory integration is infrequent in the blind field of patients with hemianopia
Are language production problems apparent in adults who no longer meet diagnostic criteria for attention-deficit/hyperactivity disorder?
No full textIn this study, we examined sentence production in a sample of adults (N = 21) who had had attention-deficit/hyperactivity disorder (ADHD) as children, but as adults no longer met DSM-IV diagnostic criteria (APA, 2000). This “remitted” group was assessed on a sentence production task. On each trial, participants saw two objects and a verb. Their task was to construct a sentence using the objects as arguments of the verb. Results showed more ungrammatical and disfluent utterances with one particular type of verb (i.e., participle). In a second set of analyses, we compared the remitted group to both control participants and a “persistent” group, who had ADHD as children and as adults. Results showed that remitters were more likely to produce ungrammatical utterances and to make repair disfluencies compared to controls, and they patterned more similarly to ADHD participants. Conclusions focus on language output in remitted ADHD, and the role of executive functions in language production
Current concepts on oxidative/carbonyl stress, inflammation and epigenetics in pathogenesis of chronic obstructive pulmonary disease
No full textChronic obstructive pulmonary disease (COPD) is a global health problem. The current therapies for COPD are poorly effective and the mainstays of pharmacotherapy are bronchodilators. A better understanding of the pathobiology of COPD is critical for the development of novel therapies. In the present review, we have discussed the roles of oxidative/aldehyde stress, inflammation/immunity, and chromatin remodeling in the pathogenesis of COPD. An imbalance of oxidants/antioxidants caused by cigarette smoke and other pollutants/biomass fuels plays an important role in the pathogenesis of COPD by regulating redox-sensitive transcription factors (e.g., NF-κB), autophagy and unfolded protein response leading to chronic lung inflammatory response. Cigarette smoke also activates canonical/alternative NF-κB pathways and their upstream kinases leading to sustained inflammatory response in lungs. Recently, epigenetic regulation has been shown to be critical for the development of COPD because the expression/activity of enzymes that regulate these epigenetic modifications have been reported to be abnormal in airways of COPD patients. Hence, the significant advances made in understanding the pathophysiology of COPD as described herein will identify novel therapeutic targets for intervention in COPD
Humans as a model for understanding biological fundamentals
No full textThis is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this record.How special are humans? This question drives scholarly output across both the sciences and the humanities. Whereas some disciplines, and the humanities in particular, aim at gaining a better understanding of humans per se, most biologists ultimately aim to understand life in general. This raises the question of whether and when humans are acceptable, or even desirable, models of biological fundamentals. Especially for basic biological processes, non-human species are generally accepted as a relevant model to study topics for which studying humans is impractical, impossible, or ethically inadvisable, but the reverse is controversial: Are humans “too unique” to be informative with respect to biological fundamentals relevant to other species? Or are there areas where they share key components, or for which our very uniqueness serves to allow novel explorations? In this special feature, authors from disciplines including biology, psychology, anthropology, neuroscience, and philosophy tackle this question. Their overall conclusion is a qualified yes: humans do tell us about biological fundamentals, in some contexts. We hope this Special Feature will spur a discussion that will lead to a more careful delineation of the similarities and the differences between humans and other species, and how these impact the study of biological fundamentals.During the writing of this manuscript, SFB was supported in part by NSF grants SES 1123897 and SES 1425216 and EP by Swiss National Science Foundation grant 31003A_159462
Deletion of vitamin D receptor leads to premature emphysema/COPD by increased matrix metalloproteinases and lymphoid aggregates formation
No full textDeficiency of vitamin D is associated with accelerated decline in lung function. Vitamin D is a ligand for nuclear hormone vitamin D receptor (VDR), and upon binding it modulates various cellular functions. The level of VDR is reduced in lungs of patients with chronic obstructive pulmonary disease (COPD) which led us to hypothesize that deficiency of VDR leads to significant alterations in lung phenotype that are characteristics of COPD/emphysema associated with increased inflammatory response. We found that VDR knock-out (VDR(-/-)) mice had increased influx of inflammatory cells, phospho-acetylation of nuclear factor-kappaB (NF-κB) associated with increased proinflammatory mediators, and up-regulation of matrix metalloproteinases (MMPs) MMP-2, MMP-9, and MMP-12 in the lung. This was associated with emphysema and decline in lung function associated with lymphoid aggregates formation compared to WT mice. These findings suggest that deficiency of VDR in mouse lung can lead to an early onset of emphysema/COPD because of chronic inflammation, immune dysregulation, and lung destruction
- …
