10,066 research outputs found
KNEE SEPARATION DISTANCE AND QUADRICEPS AND HAMSTRINGS STRENGTH DURING DROP VERTICAL JUMP LANDINGS
Non-contact anterior cruciate ligament (ACL) injury is common particularly in female athletes during jump landing tasks. Ligament dominance occurs when the muscles cannot control knee movement sufficiently thus increasing medial knee motion. Preferential use of the quadriceps during landing and greater strength compared to the hamstrings also increase the load placed on the ACL (Dugan, 2005). Noyes et al. (2005) measured knee separation distance during jump landings finding an increase after neuromuscular training. The aim of this study was to examine the relationship between knee separation distance during drop jump landing and hamstrings and quadriceps strength in female athletes
Asymptotically exact mean field theory for the Anderson model including double occupancy
The Anderson impurity model for finite values of the Coulomb repulsion is
studied using a slave boson representation for the empty and doubly occupied
-level. In order to avoid well known problems with a naive mean field theory
for the boson fields, we use the coherent state path integral representation to
first integrate out the double occupancy slave bosons. The resulting effective
action is linearized using {\bf two-time} auxiliary fields. After integration
over the fermionic degrees of freedom one obtains an effective action suitable
for a -expansion. Concerning the constraint the same problem remains as
in the infinite case. For and
exact results for the ground state properties are recovered in the saddle point
approximation. Numerical solutions of the saddle point equations show that even
in the spindegenerate case the results are quite good.Comment: 19, RevTeX, cond-mat/930502
Breathers in the elliptic sine-Gordon model
We provide new expressions for the scattering amplitudes in the
soliton-antisoliton sector of the elliptic sine-Gordon model in terms of cosets
of the affine Weyl group corresponding to infinite products of q-deformed gamma
functions. When relaxing the usual restriction on the coupling constants, the
model contains additional bound states which admit an interpretation as
breathers. These breather bound states are unavoidably accompanied by Tachyons.
We compute the complete S-matrix describing the scattering of the breathers
amonst themselves and with the soliton-antisoliton sector. We carry out various
reductions of the model, one of them leading to a new type of theory, namely an
elliptic version of the minimal D(n+1)-affine Toda field theory.Comment: 20 pages, Latex, one eps-figur
Classification and Stability of Phases of the Multicomponent One-Dimensional Electron Gas
The classification of the ground-state phases of complex one-dimensional
electronic systems is considered in the context of a fixed-point strategy.
Examples are multichain Hubbard models, the Kondo-Heisenberg model, and the
one-dimensional electron gas in an active environment. It is shown that, in
order to characterize the low-energy physics, it is necessary to analyze the
perturbative stability of the possible fixed points, to identify all discrete
broken symmetries, and to specify the quantum numbers and elementary wave
vectors of the gapless excitations. Many previously-proposed exotic phases of
multichain Hubbard models are shown to be unstable because of the ``spin-gap
proximity effect.'' A useful tool in this analysis is a new generalization of
Luttinger's theorem, which shows that there is a gapless even-charge mode in
any incommensurate N-component system.Comment: 15 pages revtex. Final version as publishe
The break up of heavy electrons at a quantum critical point
The point at absolute zero where matter becomes unstable to new forms of
order is called a quantum critical point (QCP). The quantum fluctuations
between order and disorder that develop at this point induce profound
transformations in the finite temperature electronic properties of the
material. Magnetic fields are ideal for tuning a material as close as possible
to a QCP, where the most intense effects of criticality can be studied. A
previous study on theheavy-electron material found that near a
field-induced quantum critical point electrons move ever more slowly and
scatter off one-another with ever increasing probability, as indicated by a
divergence to infinity of the electron effective mass and cross-section. These
studies could not shed light on whether these properties were an artifact of
the applied field, or a more general feature of field-free QCPs. Here we report
that when Germanium-doped is tuned away from a chemically induced
quantum critical point by magnetic fields there is a universal behavior in the
temperature dependence of the specific heat and resistivity: the characteristic
kinetic energy of electrons is directly proportional to the strength of the
applied field. We infer that all ballistic motion of electrons vanishes at a
QCP, forming a new class of conductor in which individual electrons decay into
collective current carrying motions of the electron fluid.Comment: Pdf files of article available at
http://www.physics.rutgers.edu/~coleman/online/breakup.pdf, pdf file of news
and views article available at
http://www.physics.rutgers.edu/~coleman/online/nvbreakup.pd
Analysis of No-Difference Findings in Evaluation Research
Conclusions of no difference are becoming increasingly important in evaluation research. We delineate three major uses of no-difference findings and analyze their meanings. (1) No-differ ence findings in randomized experiments can be interpreted as support for conclusions of the absence of a meaningful treatment effect, but only if the proper analytic methods are used. (2) Statistically based conclusions in quasi-experiments do not allow causal statements about the treatment impact but do provide a metric to judge the size of the resulting difference. (3) Using no-difference findings to conclude equivalence on control variables is inefficient and potentially misleading. The final section of the article presents alternative methods by which conclusions of no difference may be supported when applicable. These methods include the use of arbitrarily high alpha levels, interval estimation, and power analysis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67182/2/10.1177_0193841X8901300604.pd
Effective String Theory Revisited
We revisit the effective field theory of long relativistic strings such as
confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by
a calculation in static gauge. This interaction implies that a non-critical
string which initially oscillates in one direction gets excited in orthogonal
directions as well. In static gauge no additional term in the effective action
is needed to obtain this effect. It results from a one-loop calculation using
the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at
all stages in dimensional regularization. We also explain that independent of
the number of dimensions non-covariant counterterms have to be added to the
action in the commonly used zeta-function regularization.Comment: 21 pages, 4 figures, v2: typo corrected, references added, published
versio
Co-operative Kondo Effect in the two-channel Kondo Lattice
We discuss the possibility of a co-operative Kondo effect driven by channel
interference in a Kondo lattice where local moments are coupled to a single
Fermi sea via two orthogonal scattering channels. In this situation, the
channel quantum number is not conserved. We argue that the absence of channel
conservation causes the Kondo effect in the two channels to constructively
interfere, giving rise to a superconducting condensate of composite pairs,
formed between the local moments and the conduction electrons. Our arguments
are based on the observation that a heavy Fermi surface gives rise to zero
modes for Kondo singlets to fluctuate between screening channels of different
symmetry, producing a divergent composite pair susceptibility. Secondary
screening channels couple to these divergent fluctuations, promoting an
instability into a state with long-range composite order. We present detailed a
detailed mean-field theory for this superconducting phase, and discuss the
possible implications for heavy fermion physics.Comment: 23 double column pages. 9 fig
Chiral Lagrangians
An overview of the field of Chiral Lagrangians is given. This includes Chiral
Perturbation Theory and resummations to extend it to higher energies,
applications to the muon anomalous magnetic moment,
and others.Comment: Invited talk at the XX International Symposium on Lepton and Photon
Interactions at High Energies 23rd-28th July 2001, Rome Italy, 15 pages, uses
ws-p10x7.cls Changes: 2 references added, numbers in g-2 hadronic changed
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