32 research outputs found
Extrapyramidal signs in normal pressure hydrocephalus: an objective assessment
<p>Abstract</p> <p>Background</p> <p>Beyond the classic Normal Pressure Hydrocephalus (NPH) triad of gait disturbance, incontinence, and dementia are characteristic signs of motor dysfunction in NPH patients. We used highly sensitive and objective methods to characterize upper limb extrapyramidal signs in a series of NPH subjects compared with controls. Concentrated evaluation of these profound, yet underappreciated movement disorders of NPH before and after techniques of therapeutic intervention may lead to improved diagnosis, insight into pathophysiology, and targeted treatment.</p> <p>Methods</p> <p>Twenty-two (22) consecutive NPH patients and 17 controls performed an upper limb motor task battery where highly sensitive and objective measures of akinesia/bradykinesia, tone, and tremor were conducted. NPH subjects performed this test battery before and more than 36 h after continuous CSF drainage via a spinal catheter over 72 h and, in those subjects undergoing permanent ventriculo-peritoneal shunt placement, at least 12 weeks later. Control subjects performed the task battery at the same dates as the NPH subjects. Statistical analyses were applied to group populations of NPH and control subjects and repeated measures for within subject performance.</p> <p>Results</p> <p>Twenty (20) NPH subjects remained in the study following CSF drainage as did 14 controls. NPH subjects demonstrated akinesia/bradykinesia (prolonged reaction and movement times) and increased resting tone compared with controls. Furthermore, the NPH group demonstrated increased difficulty with self-initiated tasks compared with stimulus-initiated tasks. Following CSF drainage, some NPH subjects demonstrated reduced movement times with greater improvement in self- versus stimulus-initiated tasks. Group reaction time was unchanged. Resting tremor present in one NPH subject resolved following shunt placement. Tone measures were consistent for all subjects throughout the study.</p> <p>Conclusion</p> <p>Clinical motor signs of NPH subjects extend beyond gait deficits and include extrapyramidal manifestations of bradykinesia, akinesia, rigidity, and propensity to perform more poorly when external cues to move are absent. Objective improvement of some but not all of these features was seen following temporary or permanent CSF diversion.</p
Towards a holographic dual of large-N_c QCD
We study N_f D6-brane probes in the supergravity background dual to N_c
D4-branes compactified on a circle with supersymmetry-breaking boundary
conditions. In the limit in which the resulting Kaluza--Klein modes decouple,
the gauge theory reduces to non-supersymmetric, four-dimensional QCD with N_c
colours and N_f << N_c flavours. As expected, this decoupling is not fully
realised within the supergravity/Born--Infeld approximation. For N_f = 1 and
massless quarks, m_q = 0, we exhibit spontaneous chiral symmetry breaking by a
quark condensate, \neq 0, and find the associated massless
`pion' in the spectrum. The latter becomes massive for m_q > 0, obeying the
Gell-Mann--Oakes--Renner relation: M_pi^2= - m_q / \f_pi^2. In
the case N_f > 1 we provide a holographic version of the Vafa--Witten theorem,
which states that the U(N_f) flavour symmetry cannot be spontaneously broken.
Further we find N_f^2 - 1 unexpectedly light pseudo-scalar mesons in the
spectrum. We argue that these are not (pseudo) Goldstone bosons and speculate
on the string mechanism responsible for their lightness. We then study the
theory at finite temperature and exhibit a phase transition associated with a
discontinuity in the chiral condensate. D6/anti-D6 pairs are also briefly
discussed.Comment: 43 pages, LaTeX; v3: Scalar vs. pseudo-scalar nature of mesons
clarified, references added. v4: Small change in Acknowledgment
Non-holomorphic Corrections from Threebranes in F Theory
We construct solutions of type IIB supergravity dual to N=2 super Yang-Mills
theories. By considering a probe moving in a background with constant coupling
and an AdS_{5} component in its geometry, we are able to reproduce the exact
low energy effective action for the theory with gauge group SU(2) and N_{f}=4
massless flavors. After turning on a mass for the flavors we find corrections
to the AdS_{5} geometry. In addition, the coupling shows a power law dependence
on the energy scale of the theory. The origin of the power law behaviour of the
coupling is traced back to instanton corrections. Instanton corrections to the
four derivative terms in the low energy effective action are correctly obtained
from a probe analysis. By considering a Wilson loop in this geometry we are
also able to compute the instanton effects on the quark-antiquark potential.
Finally we consider a solution corresponding to an asymptotically free field
theory. Again, the leading form of the four derivative terms in the low energy
effective action are in complete agreement with field theory expectations.Comment: 23 pages, uses harvmac, References added, typos corrected and minor
improvements to discussion of N dependence, to appear in Phys. Rev.
Meson Spectroscopy in AdS/CFT with Flavour
We compute the meson spectrum of an N=2 super Yang-Mills theory with
fundamental matter from its dual string theory on AdS_5 x S_5 with a D7-brane
probe. For scalar and vector mesons with arbitrary R-charge the spectrum is
computed in closed form by solving the equations for D7-brane fluctuations; for
matter with non-zero mass m_q it is discrete, exhibits a mass gap of order m_q
/ sqrt(g_s N) and furnishes representations of SO(5) even though the manifest
global symmetry of the theory is only SO(4). The spectrum of mesons with large
spin J is obtained from semiclassical, rotating open strings attached to the
D7-brane. It displays Regge-like behaviour for J << sqrt(g_s N), whereas for J
>> sqrt(g_s N) it corresponds to that of two non-relativistic quarks bound by a
Coulomb potential. Meson interactions, baryons and `giant gauge bosons' are
briefly discussed.Comment: LaTeX, 39 pages, 4 figures, uses epsf. v2: typos corrected.
references adde
Beyond the Planar Limit in ABJM
In this article we consider gauge theories with a U(N)X U(N) gauge group. We
provide, for the first time, a complete set of operators built from scalar
fields that are in the bi fundamental of the two groups. Our operators
diagonalize the two point function of the free field theory at all orders in
1/N. We then use this basis to investigate non-planar anomalous dimensions in
the ABJM theory. We show that the dilatation operator reduces to a set of
decoupled harmonic oscillators, signaling integrability in a nonplanar large N
limit.Comment: v2: minor revisison
Giant Gravitons - with Strings Attached (III)
We develop techniques to compute the one-loop anomalous dimensions of
operators in the super Yang-Mills theory that are dual to open
strings ending on boundstates of sphere giant gravitons. Our results, which are
applicable to excitations involving an arbitrary number of open strings,
generalize the single string results of hep-th/0701067. The open strings we
consider carry angular momentum on an S embedded in the S of the
AdSS background. The problem of computing the one loop anomalous
dimensions is replaced with the problem of diagonalizing an interacting Cuntz
oscillator Hamiltonian. Our Cuntz oscillator dynamics illustrates how the
Chan-Paton factors for open strings propagating on multiple branes can arise
dynamically.Comment: 66 pages; v2: improved presentatio
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
Implications of Anomaly Constraints in the -Extended Standard Model
We discuss some implications of anomaly cancellation in the standard model
with (i) the color group extended to , and (ii) the leptonic sector
extended to allow right-handed components for neutrinos.Comment: 26 pages, late
Giant Graviton Oscillators
We study the action of the dilatation operator on restricted Schur
polynomials labeled by Young diagrams with p long columns or p long rows. A new
version of Schur-Weyl duality provides a powerful approach to the computation
and manipulation of the symmetric group operators appearing in the restricted
Schur polynomials. Using this new technology, we are able to evaluate the
action of the one loop dilatation operator. The result has a direct and natural
connection to the Gauss Law constraint for branes with a compact world volume.
We find considerable evidence that the dilatation operator reduces to a
decoupled set of harmonic oscillators. This strongly suggests that
integrability in N=4 super Yang-Mills theory is not just a feature of the
planar limit, but extends to other large N but non-planar limits.Comment: 72 page