1,923 research outputs found
Reply to "Comment on 'Precision measurement of the Casimir-Lifshitz force in a fluid'"
We have reviewed the Comment of Geyer et al. [arXiv:0708.1548] concerning our
recent work [Phys. Rev. A 75, 060102 (R) (2007)], and while we disagree with
their criticisms, we acknowledge them for giving us the opportunity to add
interesting addition material and a more detailed description of our
experiment. We describe further our calculation and explain why a more
sophisticated model is not warranted. We also present detailed experiments on
the effects of electrostatic forces in our measurements and show that the
contribution due to work function differences is small and that the residual
electrostatic force is dominated by trapped charges and external fields.
Finally, we estimate the effect of double layer interactions. These additional
calculations and measurements support our original conclusion that the
experimental results are consistent with the Lifshitz theory
Role of Schizosaccharomyces pombe RecQ homolog recombination and checkpoint genes in UV Damage tolerance
The cellular responses to DNA damage are complex and include direct DNA repair pathways that remove the damage and indirect damage responses which allow cells to survive DNA damage that has not been, or cannot be, removed. We have identified the gene mutated in the rad12.502 strain as a Schizosaccharomyces pombe recQ homolog. The same gene (designated rqh1) is also mutated in the hus2.22 mutant. We show that Rqh1 is involved in a DNA damage survival mechanism which prevents cell death when UV-induced DNA damage cannot be removed. This pathway also requires the correct functioning of the recombination machinery and the six checkpoint tad gene products plus the Cds1 kinase. Our data suggest that Rqh1 operates during S phase as part of a mechanism which prevents DNA damage causing cell lethality. This process may involve the bypass of DNA damage sites by the replication fork. Finally, in contrast with the reported literature, we do not find that rqh1 (rad12) mutant cells are defective in UV dimer endonuclease activity
Quantum electrodynamical torques in the presence of Brownian motion
Quantum fluctuations of the electromagnetic field give rise to a zero-point energy that persists even in the absence of electromagnetic sources. One striking consequence of the zero-point energy is manifested in the Casimir force, which causes two electrically neutral metallic plates to attract in order to reduce the zero-point energy. A second, less well-known, effect is a torque that arises between two birefringent materials with in-plane optical anisotropy as a result of the zero-point energy. In this paper, we discuss the influence of Brownian motion on two birefringent plates undergoing quantum electrodynamical (QED) rotation as a result of the system's zero-point energy. Direct calculations for the torque are presented, and preliminary experiments are discussed. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Precision measurement of the Casimir-Lifshitz force in a fluid
The Casimir force, which results from the confinement of the quantum
mechanical zero-point fluctuations of the electromagnetic fields, has received
significant attention in recent years for its effect on micro- and nano-scale
mechanical systems. With few exceptions, experimental observations have been
limited to conductive bodies interacting separated by vacuum or air. However,
interesting phenomena including repulsive forces are expected to exist in
certain circumstances between metals and dielectrics when the intervening
medium is not vacuum. In order to better understand the effect of the Casimir
force in such situations and to test the robustness of the generalized
Casimir-Lifshitz theory, we have performed the first precision measurements of
the Casimir force between two metals immersed in a fluid. For this situation,
the measured force is attractive and is approximately 80% smaller than the
force predicted by Casimir for ideal metals in vacuum. We present experimental
results and find them to be consistent with Lifshitz's theory.Comment: 6 pages, 3 figures. (version before final publication
Stable suspension and dispersion-induced transitions from repulsive Casimir forces between fluid-separated eccentric cylinders
Using an exact numerical method for finite nonplanar objects, we demonstrate
a stable mechanical suspension of a silica cylinder within a metallic cylinder
separated by ethanol, via a repulsive Casimir force between the silica and the
metal. We investigate cylinders with both circular and square cross sections,
and show that the latter exhibit a stable orientation as well as a stable
position, via a method to compute Casimir torques for finite objects.
Furthermore, the stable orientation of the square cylinder is shown to undergo
an unusual 45 degrees transition as a function of the separation lengthscale,
which is explained as a consequence of material dispersion.Comment: Published in Physical Review Letters. Vol. 101, page, 190404 (2008
Trypanosoma brucei bloodstream forms express highly specific and separate transporters for adenine and hypoxanthine; evidence for a new protozoan purine transporter family?
The transport of nucleobases and nucleosides in protozoan parasites is known to be performed by Equilibrative Nucleoside Transporter (ENT) family members, including the extensively studied P1 and P2 nucleoside transporters of T. brucei bloodstream forms. Studies with P2 knockout parasites suggested the existence of as yet uncharacterised purine transport mechanisms in these cells. Here, we deleted several ENT genes, in addition to P2, including an array comprising three genes encoding for high-affinity broad-selectivity nucleobase transporters - the longest multi-gene locus deletion in T. brucei to date. It was verified that none of them appreciably contributed to the transport of hypoxanthine in bloodstream forms grown axenically in HMI-9 medium, which was mainly performed by a previously not described hypoxanthine-specific transporter (HXT1) with a Km of 22 ± 1.7 μM and Vmax of 0.49 ± 0.06 pmol(107 cells)-1s-1. The uptake of adenine was also assessed in the knockout cells and was performed by a highly specific adenine transporter (ADET1) with a Km of 573 ± 62 nM and Vmax of 0.23 ± 0.06 pmol(107 cells)-1 s-1. Neither HXT1 nor ADET1 displayed any affinity for other natural purines or pyrimidines and could not be completely inhibited by hypoxanthine or adenine analogues. These carriers may be the final pieces in the substantial transporter array trypanosomes can employ to fine-tune the uptake of purines from diverse environments during their life cycles, and may be encoded by genes other than those of the ENT family
Prioriy Problems and Data Needs in Coastal Zone Oceanography Earth Observation Satellite Planning
Coastal zone oceanographic problems and data needs have been defined for an oceanographic satellite. Problems are based on national and coastal zone priorities. Descriptions of the problems discuss the data needs and the expected utility of remote measurement. Data needs and resolution requirements are specified for surface and satellite measurement. Remote measurables are numerically ranked and evaluated. Coordination of the ERTS program with DOE is discussed
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Towards improved socio-economic assessments of ocean acidification’s impacts
Ocean acidification is increasingly recognized as a component of global change that could have a wide range of impacts on marine organisms, the ecosystems they live in, and the goods and services they provide humankind. Assessment of these potential socio-economic impacts requires integrated efforts between biologists, chemists, oceanographers, economists and social scientists. But because ocean acidification is a new research area, significant knowledge gaps are preventing economists from estimating its welfare impacts. For instance, economic data on the impact of ocean acidification on significant markets such as fisheries, aquaculture and tourism are very limited (if not non-existent), and non-market valuation studies on this topic are not yet available. Our paper summarizes the current understanding of future OA impacts and sets out what further information is required for economists to assess socio-economic impacts of ocean acidification. Our aim is to provide clear directions for multidisciplinary collaborative research
Learning to work together - lessons from a reflective analysis of a research project on public involvement
Abstract
Background Patient and public involvement (PPI) is now an expectation of research
funders, in the UK, but there is relatively little published literature on what this means in
practice – nor is there much evaluative research about implementation and outputs.
Policy literature endorses the need to include PPI representation at all stages of
planning, performing and research dissemination, and recommends resource allocation
to these roles; but details of how to make such inputs effective in practice are less
common. While literature on power and participation informs the debate, there are
relatively few published case studies of how this can play out through the lived experience of PPI in research; early findings highlight key issues around access to
knowledge, resources, and interpersonal respect. This article describes the findings of a
case study of PPI within a study about PPI in research.
Methods The aim of the study was to look at how the PPI representatives’ inputs had
developed over time, key challenges and changes, and lessons learned. We used realist
evaluation and normalisation process theory to frame and analyse the data, which was
drawn from project documentation, minutes of meetings and workshops, field notes
and observations made by PPI representatives and researchers; documented feedback
after meetings and activities; and the structured feedback from two formal reflective
meetings.
Findings Key findings included the need for named contacts who support, integrate
and work with PPI contributors and researchers, to ensure partnership working is
encouraged and supported to be as effective as possible. A structure for partnership
working enabled this to be enacted systematically across all settings. Some individual
tensions were nonetheless identified around different roles, with possible implications
for clarifying expectations and deepening understandings of the different types of PPI
contribution and of their importance. Even in a team with research expertise in PPI, the
data showed that there were different phases and challenges to ‘normalising’ the PPI
input to the project. Mutual commitment and flexibility, embedded through
relationships across the team, led to inclusion and collaboration.
Conclusion Work on developing relationships and teambuilding are as important for
enabling partnership between PPI representatives and researchers as more practical
components such as funding and information sharing. Early explicit exploration of the
different roles and their contributions may assist effective participation and satisfaction
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