11,294 research outputs found
One qubit almost completely reveals the dynamics of two
From the time dependence of states of one of them, the dynamics of two
interacting qubits is determined to be one of two possibilities that differ
only by a change of signs of parameters in the Hamiltonian. The only exception
is a simple particular case where several parameters in the Hamiltonian are
zero and one of the remaining nonzero parameters has no effect on the time
dependence of states of the one qubit. The mean values that describe the
initial state of the other qubit and of the correlations between the two qubits
also are generally determined to within a change of signs by the time
dependence of states of the one qubit, but with many more exceptions. An
example demonstrates all the results. Feedback in the equations of motion that
allows time dependence in a subsystem to determine the dynamics of the larger
system can occur in both classical and quantum mechanics. The role of quantum
mechanics here is just to identify qubits as the simplest objects to consider
and specify the form that equations of motion for two interacting qubits can
take.Comment: 6 pages with new and updated materia
Experimental muscle pain increases normalized variability of multidirectional forces during isometric contractions
Pain elicits complex adaptations of motor strategy, leading to impairments in the generation and control of steady forces, which depend on muscle architecture. The present study used a cross-over design to assess the effects of muscle pain on the stability of multidirectional (taskrelated and tangential) forces during sustained dorsiflexions, elbow flexions, knee extensions, and plantarflexions. Fifteen healthy subjects performed series of isometric contractions (13-s duration, 2.5, 20, 50, 70% of maximal voluntary force) before, during, and after experimental muscle pain. Three-dimensional force magnitude, angle and variability were measured while the task-related force was provided as feedback to the subjects. Surface electromyography was recorded from agonist and antagonist muscles. Pain was induced in agonist muscles by intramuscular injections of hypertonic (6%) saline with isotonic (0.9%) saline injections as control. The pain intensity was assessed on an electronic visual analogue scale. Experimental muscle pain elicited larger ranges of force angle during knee extensions and plantarflexions (P < 0.03) and higher normalized fluctuations of task-related (P < 0.02) and tangential forces (P < 0.03) compared with control assessments across force levels, while the mean force magnitudes, mean force angle and the level of muscle activity were non-significantly affected by pain. Increased multidirectional force fluctuations probably resulted from multiple mechanisms that, acting together, balanced the mean surface electromyography. Although pain adaptations are believed to aim at the protection of the painful site, the current results show that they result in impairments in steadiness of force
Law Behind Second Law of Thermodynamics --Unification with Cosmology--
In an abstract setting of a general classical mechanical system as a model
for the universe we set up a general formalism for a law behind the second law
of thermodynamics, i.e. really for "initial conditions". We propose a
unification with the other laws by requiring similar symmetry and locality
properties.Comment: 17 page
Medial Prefrontal Transcranial Direct Current Stimulation Aimed to Improve Affective and Attentional Modulation of Pain in Chronic Low Back Pain Patients
Chronic low back pain (CLBP) is often without clear underlying pathology. Affective disturbance and dysfunctional pain mechanisms, commonly observed in populations with CLBP, have, therefore, been suggested as potential contributors to CLBP development and maintenance. However, little consensus exists on how these features interact and if they can be targeted using non-invasive brain stimulation. In this pilot trial, 12 participants completed two phases (Active or Sham) of high-definition transcranial direct current stimulation (HD-tDCS) to the medial prefrontal cortex, applied for 20 min on three consecutive days. Clinical pain ratings, questionnaires, and sensitivity to painful cuff pressure were completed at baseline, then 4 trials of conditioned pain modulation (CPM; alone, with distraction using a Flanker task, with positive affect induction, and with negative affect induction using an image slideshow) were performed prior to HD-tDCS on Day 1 and Day 4 (24 h post-HD-tDCS). At baseline, attentional and affective manipulations were effective in inducing the desired state (p p < 0.02) but also showed poor reliability across days. Future work is needed to expand upon these findings and better understand how and if HD-tDCS can be used to enhance attentional and affective effects on pain modulation
Acid-induced experimental muscle pain and hyperalgesia with single and repeated infusion in human forearm
Abstract
Background and purpose
Acid has long been thought to play an important role in the pain process. Animal study showed that repeated acid stimulation induced central sensitization. The purpose of the study is to investigate muscle pain and hyperalgesia evoked byintramuscular infusion of saline at different pH levels, and to compare the effect of a single versus repeated acid infusions.
Methods
Twenty healthy subjects received infusions of buffered saline (pH 5.0, 6.0, and 7.4) into the brachioradialis muscle in a randomized order. Twelve of the subjects received repeated infusions. The subjects rated the pain intensity on visual analogue scale (VAS). Thermal pain sensitivity, and pressure pain threshold (PPT) were assessed in both arm before, during, immediately after, one hour after, and one day after the infusion. A McGill Pain Questionnaire and pain mapping were completed after each infusion.
Results
The pH 5 solution caused significantly higher pain and larger areas than pH 6.0 or 7.4. The local PPTs were significantly decreased (hyperalgesia) during and immediately after infusion of all three solutions. No significant differences were detected between the first and second infusion.
Conclusions
The intensity of acid-induced muscle pain is pH-dependent. All three solutions induced pressure hyperalgesia at the infusion site. Repeated infusions did not induce increased pain or prolonged hyperalgesia as compared with a single injection. Human intramuscular acidic saline infusion could not produce chronic pain model.
Implications
The acid-induced pain model may reflect the early stage responses to tissue injury of clinical conditions. Repeated intramuscular acidic saline injection model of prolonged hyperalgesia in rodents could not be translated into a human for modelling chronic musculoskeletal pain.
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Model Independent Tests of Skyrmions and Their Holographic Cousins
We describe a new exact relation for large QCD for the long-distance
behavior of baryon form factors in the chiral limit. This model-independent
relation is used to test the consistency of the structure of several baryon
models. All 4D semiclassical chiral soliton models satisfy the relation, as
does the Pomarol-Wulzer holographic model of baryons as 5D Skyrmions. However,
remarkably, we find that the holographic model treating baryons as instantons
in the Sakai-Sugimoto model does not satisfy the relation.Comment: v2. Added references, corrected typo
Cloning and Joint Measurements of Incompatible Components of Spin
A joint measurement of two observables is a {\it simultaneous} measurement of
both quantities upon the {\it same} quantum system. When two quantum-mechanical
observables do not commute, then a joint measurement of these observables
cannot be accomplished by projective measurements alone. In this paper we shall
discuss the use of quantum cloning to perform a joint measurement of two
components of spin associated with a qubit system. We introduce a cloning
scheme which is optimal with respect to this task. This cloning scheme may be
thought to work by cloning two components of spin onto its outputs. We compare
the proposed cloning machine to existing cloners.Comment: 7 pages, 2 figures, submitted to PR
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