7,300 research outputs found
Microscopic theory of the quantum Hall hierarchy
We solve the quantum Hall problem exactly in a limit and show that the ground
states can be organized in a fractal pattern consistent with the
Haldane-Halperin hierarchy, and with the global phase diagram. We present wave
functions for a large family of states, including those of Laughlin and Jain
and also for states recently observed by Pan {\it et. al.}, and show that they
coincide with the exact ones in the solvable limit. We submit that they
establish an adiabatic continuation of our exact results to the experimentally
accessible regime, thus providing a unified approach to the hierarchy states.Comment: 4 pages, 2 figures. Publishe
Context-dependent deactivation of the amygdala during pain
The amygdala has been implicated in fundamental functions for the survival of the organism, such as fear and pain. In accord with this, several studies have shown increased amygdala activity during fear conditioning and the processing of fear-relevant material in human subjects. In contrast, functional neuroimaging studies of pain have shown a decreased amygdala activity. It has previously been proposed that the observed deactivations of the amygdala in these studies indicate a cognitive strategy to adapt to a distressful but in the experimental setting unavoidable painful event. In this positron emission tomography study, we show that a simple contextual manipulation, immediately preceding a painful stimulation, that increases the anticipated duration of the painful event leads to a decrease in amygdala activity and modulates the autonomic response during the noxious stimulation. On a behavioral level, 7 of the 10 subjects reported that they used coping strategies more intensely in this context. We suggest that the altered activity in the amygdala may be part of a mechanism to attenuate pain-related stress responses in a context that is perceived as being more aversive. The study also showed an increased activity in the rostral part of anterior cingulate cortex in the same context in which the amygdala activity decreased, further supporting the idea that this part of the cingulate cortex is involved in the modulation of emotional and pain network
Transition from sea to land: olfactory function and constraints in the terrestrial hermit crab Coenobita clypeatus
The ability to identify chemical cues in the environment is essential to most animals. Apart from marine larval stages, anomuran land hermit crabs (Coenobita) have evolved different degrees of terrestriality, and thus represent an excellent opportunity to investigate adaptations of the olfactory system needed for a successful transition from aquatic to terrestrial life. Although superb processing capacities of the central olfactory system have been indicated in Coenobita and their olfactory system evidently is functional on land, virtually nothing was known about what type of odourants are detected. Here, we used electroantennogram (EAG) recordings in Coenobita clypeatus and established the olfactory response spectrum. Interestingly, different chemical groups elicited EAG responses of opposite polarity, which also appeared for Coenobita compressus and the closely related marine hermit crab Pagurus bernhardus. Furthermore, in a two-choice bioassay with C. clypeatus, we found that water vapour was critical for natural and synthetic odourants to induce attraction or repulsion. Strikingly, also the physiological response was found much greater at higher humidity in C. clypeatus, whereas no such effect appeared in the terrestrial vinegar fly Drosophila melanogaster. In conclusion, our results reveal that the Coenobita olfactory system is restricted to a limited number of water-soluble odourants, and that high humidity is most critical for its function
Quantum Hall quasielectron operators in conformal field theory
In the conformal field theory (CFT) approach to the quantum Hall effect, the
multi-electron wave functions are expressed as correlation functions in certain
rational CFTs. While this approach has led to a well-understood description of
the fractionally charged quasihole excitations, the quasielectrons have turned
out to be much harder to handle. In particular, forming quasielectron states
requires non-local operators, in sharp contrast to quasiholes that can be
created by local chiral vertex operators. In both cases, the operators are
strongly constrained by general requirements of symmetry, braiding and fusion.
Here we construct a quasielectron operator satisfying these demands and show
that it reproduces known good quasiparticle wave functions, as well as predicts
new ones. In particular we propose explicit wave functions for quasielectron
excitations of the Moore-Read Pfaffian state. Further, this operator allows us
to explicitly express the composite fermion wave functions in the positive Jain
series in hierarchical form, thus settling a longtime controversy. We also
critically discuss the status of the fractional statistics of quasiparticles in
the Abelian hierarchical quantum Hall states, and argue that our construction
of localized quasielectron states sheds new light on their statistics. At the
technical level we introduce a generalized normal ordering, that allows us to
"fuse" an electron operator with the inverse of an hole operator, and also an
alternative approach to the background charge needed to neutralize CFT
correlators. As a result we get a fully holomorphic CFT representation of a
large set of quantum Hall wave functions.Comment: minor changes, publishe
Enabling application-level performance guarantees in network-based systems on chip by applying dataflow analysis
A growing number of applications, often with real-time requirements, are integrated on the same system on chip (SoC), in the form of hardware and software intellectual property (IP). To facilitate real-time applications, networks on chip (NoC) guarantee bounds on latency and throughput. These bounds, however, only extend to the network interfaces (NI), between the IP and the NoC. To give performance guarantees on the application level, the buffers in the NIs must be sufficiently large for the particular application. At the same time, it is imperative to minimise the size of the NI buffers, as they are major contributors to the area and power consumption of the NoC. Existing buffer-sizing methods use coarse-grained application models, based on linear traffic bounds or periodic producers and consumers, thus severely limiting their applicability. In this work, the authors propose to capture the behaviour of the NoC and the applications using a dataflow model. This enables one to verify the temporal behaviour and to compute buffer sizes using existing dataflow analysis techniques. The authors show what is required from the NoC architecture and demonstrate how to construct an NoC model, with multiple levels of detail. Using the proposed model, buffer sizes are determined for a range of SoC designs with a run time comparable to existing analytical methods, and results comparable to exhaustive simulation. For an application case study, where existing buffer-sizing methods are not applicable, the proposed model enables the verification of end-to-end temporal behaviour
Composite fermion wave functions as conformal field theory correlators
It is known that a subset of fractional quantum Hall wave functions has been
expressed as conformal field theory (CFT) correlators, notably the Laughlin
wave function at filling factor ( odd) and its quasiholes, and the
Pfaffian wave function at and its quasiholes. We develop a general
scheme for constructing composite-fermion (CF) wave functions from conformal
field theory. Quasiparticles at are created by inserting anyonic
vertex operators, , that replace a subset of the electron
operators in the correlator. The one-quasiparticle wave function is identical
to the corresponding CF wave function, and the two-quasiparticle wave function
has correct fractional charge and statistics and is numerically almost
identical to the corresponding CF wave function. We further show how to exactly
represent the CF wavefunctions in the Jain series as the CFT
correlators of a new type of fermionic vertex operators, ,
constructed from free compactified bosons; these operators provide the CFT
representation of composite fermions carrying flux quanta in the CF Landau level. We also construct the corresponding quasiparticle- and
quasihole operators and argue that they have the expected fractional charge and
statistics. For filling fractions 2/5 and 3/7 we show that the chiral CFTs that
describe the bulk wave functions are identical to those given by Wen's general
classification of quantum Hall states in terms of -matrices and - and
-vectors, and we propose that to be generally true. Our results suggest a
general procedure for constructing quasiparticle wave functions for other
fractional Hall states, as well as for constructing ground states at filling
fractions not contained in the principal Jain series.Comment: 26 pages, 3 figure
Solitons and Quasielectrons in the Quantum Hall Matrix Model
We show how to incorporate fractionally charged quasielectrons in the finite
quantum Hall matrix model.The quasielectrons emerge as combinations of BPS
solitons and quasiholes in a finite matrix version of the noncommutative
theory coupled to a noncommutative Chern-Simons gauge field. We also
discuss how to properly define the charge density in the classical matrix
model, and calculate density profiles for droplets, quasiholes and
quasielectrons.Comment: 15 pages, 9 figure
Edge Theories for Polarized Quantum Hall States
Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized state, our results agree with
previous Hartree-Fock calculations.Comment: 15 pages (number of pages has been reduced by typesetting in RevTeX);
2 references adde
Moduli-Space Dynamics of Noncommutative Abelian Sigma-Model Solitons
In the noncommutative (Moyal) plane, we relate exact U(1) sigma-model
solitons to generic scalar-field solitons for an infinitely stiff potential.
The static k-lump moduli space C^k/S_k features a natural K"ahler metric
induced from an embedding Grassmannian. The moduli-space dynamics is blind
against adding a WZW-like term to the sigma-model action and thus also applies
to the integrable U(1) Ward model. For the latter's two-soliton motion we
compare the exact field configurations with their supposed moduli-space
approximations. Surprisingly, the two do not match, which questions the
adiabatic method for noncommutative solitons.Comment: 1+15 pages, 2 figures; v2: reference added, to appear in JHE
Reasoning with comparative moral judgements: an argument for Moral Bayesianism
The paper discusses the notion of reasoning with comparative moral judgements
(i.e judgements of the form “act a is morally superior to act b”) from the point of view of several meta-ethical positions. Using a simple formal result, it is argued that only a version of moral cognitivism that is committed to the claim that moral beliefs come in degrees can give a normatively plausible account of such reasoning. Some implications of accepting such a version of moral cognitivism are discussed
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