961 research outputs found
About the Dirac Equation with a potential
An elementary treatment of the Dirac Equation in the presence of a
three-dimensional spherically symmetric -potential is
presented. We show how to handle the matching conditions in the configuration
space, and discuss the occurrence of supercritical effects.Comment: 8 pages, 1 postscript figure, Latex, Revise
An Exact String Theory Model of Closed Time-Like Curves and Cosmological Singularities
We study an exact model of string theory propagating in a space-time
containing regions with closed time-like curves (CTCs) separated from a finite
cosmological region bounded by a Big Bang and a Big Crunch. The model is an
non-trivial embedding of the Taub-NUT geometry into heterotic string theory
with a full conformal field theory (CFT) definition, discovered over a decade
ago as a heterotic coset model. Having a CFT definition makes this an excellent
laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and
the Milne/Misner-type chronology horizon which separates them. In an effort to
uncover the role of stringy corrections to such geometries, we calculate the
complete set of alpha' corrections to the geometry. We observe that the key
features of Taub-NUT persist in the exact theory, together with the emergence
of a region of space with Euclidean signature bounded by time-like curvature
singularities. Although such remarks are premature, their persistence in the
exact geometry is suggestive that string theory theory is able to make physical
sense of the Milne/Misner singularities and the CTCs, despite their
pathological character in General Relativity. This may also support the
possibility that CTCs may be viable in some physical situations, and may be a
natural ingredient in pre-Big-Bang cosmological scenarios.Comment: 37 pages, 4 figures. V2: discussion of computation of metric refined,
references adde
The influence of refractive index change and initial bending of cantilevers on the optical lever readout method
Mobility deficit â Rehabilitate, an opportunity for functionality
There are many pathological conditions that cause mobility deficits and that ultimately influence someoneâs autonomy.Aims: to evaluate patients with mobility deficits functional status; to implement a Rehabilitation Nursing intervention plan; to monitor health gains through mobility deficits rehabilitation.Conclusion: Early intervention and the implementation of a nursing rehabilitation intervention plan results in health gains (direct or indirect), decreases the risk of developing Pressure Ulcers (PU) and the risk of developing a situation of immobility that affects patientsâ autonomy and quality of life
Locality-Aware Request Distribution in Cluster-Based Network Servers
We consider cluster-based network servers in which a front-end directs incoming requests to one of a number of back-ends. Specifically, we consider content-based request distribution: the front-end uses the content requested, in addition to information about the load on the back-end nodes, to choose which back-end will handle this request. Content-based request distribution can improve locality in the back-endsâ main memory caches, increase secondary storage scalability by partitioning the serverâs database, and provide the ability to employ back-end nodes that are specialized for certain types of requests. As a specific policy for content-based request distribution, we introduce a simple, practical strategy for locality-aware request distribution (LARD). With LARD, the front-end distributes incoming requests in a manner that achieves high locality in the back-endsâ main memory caches as well as load balancing. Locality is increased by dynamically subdividing the serverâs working set over the back-ends. Trace-based simulation results and measurements on a prototype implementation demonstrate substantial performance improvements over state-of-the-art approaches that use only load information to distribute requests. On workloads with working sets that do not fit in a single server nodeâs main memory cache, the achieved throughput exceeds that of the state-of-the-art approach by a factor of two to four. With content-based distribution, incoming requests must be handed off to a back-end in a manner transparent to the client, after the front-end has inspected the content of the request. To this end, we introduce an efficient TCP handoflprotocol that can hand off an established TCP connection in a client-transparent manner
Heidegger on creativity: From boredom to re-engagement with the world
Experimental psychologists have discussed whether boredom can help us become more creative. At ïŹrst blush, this would seem to be rather unlikely. When we are bored, we are disengaged; we cannot be bothered and nothing seems worthwhile; we have no interest in the world around us. Such a condition, surely, is not conducive to creativity (Haager et al. 2018). Yet some psychologists disagree (Gasper and Middlewood 2014). Boredom, they explain, breaks down entrenched routines and thought-patterns and provides us with an opportunity to think again and anew. Respondents in âapproach-oriented statesâ such as boredom engage in more âassociative thoughtâ than those in âavoidance-oriented affective states.â This is how boredom comes to encourage âthe quest for meaning and explorationâ (Gasper and Middlewood 2014, pp. 53â55...2-s2.0-8508440789
A Note on D-brane - Anti-D-brane Interactions in Plane Wave Backgrounds
We study aspects of the interaction between a D-brane and an anti-D-brane in
the maximally supersymmetric plane wave background of type IIB superstring
theory, which is equipped with a mass parameter mu. An early such study in flat
spacetime (mu=0) served to sharpen intuition about D-brane interactions,
showing in particular the key role of the ``stringy halo'' that surrounds a
D-brane. The halo marks the edge of the region within which tachyon
condensation occurs, opening a gateway to new non-trivial vacua of the theory.
It seems pertinent to study the fate of the halo for non--zero mu. We focus on
the simplest cases of a Lorentzian brane with p=1 and an Euclidean brane with
p=-1, the D--instanton. For the Lorentzian brane, we observe that the halo is
unaffected by the presence of non--zero mu. This most likely extends to other
(Lorentzian) p. For the Euclidean brane, we find that the halo is affected by
non-zero mu. As this is related to subtleties in defining the exchange
amplitude between Euclidean branes in the open string sector, we expect this to
extend to all Euclidean branes in this background.Comment: 14 pages, LaTeX, 2 eps figures. v2: a reference and some clarifying
remarks added; v3: Considerably revised version; halo unaffected by plane
wave background for Lorentzian branes, but Euclidean branes' halo is modifie
Ultrasensitive mass sensor fully integrated with complementary metal-oxide-semiconductor circuitry
Nanomechanical resonators have been monolithically integrated on preprocessed complementary metal-oxide-semiconductor(CMOS) chips. Fabricatedresonatorsystems have been designed to have resonance frequencies up to 1.5 MHz. The systems have been characterized in ambient air and vacuum conditions and display ultrasensitive mass detection in air. A mass sensitivity of 4ag/Hz has been determined in air by placing a single glycerine drop, having a measured weight of 57 fg, at the apex of a cantilever and subsequently measuring a frequency shift of 14.8 kHz. CMOS integration enables electrostatic excitation, capacitive detection, and amplification of the resonance signal directly on the chip
Between the Natural and the Artificial: The Sublime Sexual Sensation of Car Crashes in J.G. Ballardâs Crash
At a time when technology progressively pushes back nature, the sexual act runs the risk of being denaturalised. The notion of the sublime, which I argue is how humans react to the machine as a surrogate for nature and as a sexual stimulus in Crash (1973), is therefore of central interest in this article. Ballard himself has described Crash as âthe first pornographic novel based on technologyâ (1973, 6). This engagement with a technologised sexuality is explored as a subjective narrative stance, which grants authenticity to the fictive alter ego, who can probe alternatives to an extra-textual reality. This narrative mode is notably potent in relation to the narratorâs estimation of the merge between sexuality and technology in the form of car crashes uniting Eros and Thanatos. I therefore suggest that Crash can be read as an attempt to localise the natural and human in a world dictated by artificiality and technology
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