Treatment compliance and effectiveness of a cognitive behavioural intervention for low back pain : a complier average causal effect approach to the BeST data set

Background: Group cognitive behavioural intervention (CBI) is effective in reducing low-back pain and disability in comparison to advice in primary care. The aim of this analysis was to investigate the impact of compliance on estimates of treatment effect and to identify factors associated with compliance. Methods: In this multicentre trial, 701 adults with troublesome sub-acute or chronic low-back pain were recruited from 56 general practices. Participants were randomised to advice (control n = 233) or advice plus CBI (n = 468). Compliance was specified a priori as attending a minimum of three group sessions and the individual assessment. We estimated the complier average causal effect (CACE) of treatment. Results: Comparison of the CACE estimate of the mean treatment difference to the intention-to-treat (ITT) estimate at 12 months showed a greater benefit of CBI amongst participants compliant with treatment on the Roland Morris Questionnaire (CACE: 1.6 points, 95% CI 0.51 to 2.74; ITT: 1.3 points, 95% CI 0.55 to 2.07), the Modified Von Korff disability score (CACE: 12.1 points, 95% CI 6.07 to 18.17; ITT: 8.6 points, 95% CI 4.58 to 12.64) and the Modified von Korff pain score (CACE: 10.4 points, 95% CI 4.64 to 16.10; ITT: 7.0 points, 95% CI 3.26 to 10.74). People who were non-compliant were younger and had higher pain scores at randomisation. Conclusions: Treatment compliance is important in the effectiveness of group CBI. Younger people and those with more pain are at greater risk of non-compliance

Timing Features of the Accretion--driven Millisecond X-Ray Pulsar XTE J1807--294 in 2003 March Outburst

In order to probe the activity of the inner disk flow and its effect on the neutron star surface emissions, we carried out the timing analysis of the Rossi X-Ray Timing Explorer (RXTE) observations of the millisecond X-ray pulsar XTE J1807--294, focusing on its correlated behaviors in X-ray intensities, hardness ratios, pulse profiles and power density spectra. The source was observed to have a serial of broad "puny" flares on a timescale of hours to days on the top of a decaying outburst in March 2003. In the flares, the spectra are softened and the pulse profiles become more sinusoidal. The frequency of kilohertz quasi-periodic oscillation (kHz QPO) is found to be positively related to the X-ray count rate in the flares. These features observed in the flares could be due to the accreting flow inhomogeneities. It is noticed that the fractional pulse amplitude increases with the flare intensities in a range of $\sim 2$, comparable to those observed in the thermonuclear bursts of the millisecond X-ray pulsar XTE J1814--338, whereas it remains at about 6.5% in the normal state. Such a significant variation of the pulse profile in the "puny" flares may reflect the changes of physical parameters in the inner disk accretion region. Furthermore, we noticed an overall positive correlation between the kHz QPO frequency and the fractional pulse amplitude, which could be the first evidence representing that the neutron-star surface emission properties are very sensitive to the disk flow inhomogeneities. This effect should be cautiously considered in the burst oscillation studies.Comment: Accepted by ApJ, 23 pages, 7 figures, 3 table

Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model

We suggest that the energy source of the observed diffuse gamma-ray emission from the direction of the Galactic center is the Galactic black hole Sgr A*, which becomes active when a star is captured at a rate of $\sim 10^{-5}$ yr^{-1}. Subsequently the star is tidally disrupted and its matter is accreted into the black hole. During the active phase relativistic protons with a characteristic energy $\sim 6\times 10^{52}$ erg per capture are ejected. Over 90% of these relativistic protons disappear due to proton-proton collisions on a timescale $\tau_{pp} \sim 10^4$ years in the small central bulge region with radius $\sim 50$ pc within Sgr A*, where the density is $\ge 10^3$ cm^{-3}. The gamma-ray intensity, which results from the decay of neutral pions produced by proton-proton collisions, decreases according to $e^{-t/\tau_{pp}}$, where t is the time after last stellar capture. Less than 5% of relativistic protons escaped from the central bulge region can survive and maintain their energy for >10^7 years due to much lower gas density outside, where the gas density can drop to $\sim 1$ cm$^{-3}$. They can diffuse to a $\sim 500$ pc region before disappearing due to proton-proton collisions. The observed diffuse GeV gamma-rays resulting from the decay of neutral pions produced via collision between these escaped protons and the gas in this region is expected to be insensitive to time in the multi-injection model with the characteristic injection rate of 10^{-5} yr^{-1}. Our model calculated GeV and 511 keV gamma-ray intensities are consistent with the observed results of EGRET and INTEGRAL, however, our calculated inflight annihilation rate cannot produce sufficient intensity to explain the COMPTEL data.Comment: 8 pages, 3 figures, accepted by A&

Flash-Heating of Circumstellar Clouds by Gamma Ray Bursts

The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrisic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within ~ 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions.Comment: 9 pages, 1 figure, submitted to ApJ Letter

Stochastic Process Associated with Traveling Wave Solutions of the Sine-Gordon Equation

Stochastic processes associated with traveling wave solutions of the sine-Gordon equation are presented. The structure of the forward Kolmogorov equation as a conservation law is essential in the construction and so is the traveling wave structure. The derived stochastic processes are analyzed numerically. An interpretation of the behaviors of the stochastic processes is given in terms of the equation of motion.Comment: 12 pages, 9 figures; corrected typo

Finite-level systems, Hermitian operators, isometries, and a novel parameterization of Stiefel and Grassmann manifolds

In this paper we obtain a description of the Hermitian operators acting on the Hilbert space \C^n, description which gives a complete solution to the over parameterization problem. More precisely we provide an explicit parameterization of arbitrary $n$-dimensional operators, operators that may be considered either as Hamiltonians, or density matrices for finite-level quantum systems. It is shown that the spectral multiplicities are encoded in a flag unitary matrix obtained as an ordered product of special unitary matrices, each one generated by a complex $n-k$-dimensional unit vector, $k=0,1,...,n-2$. As a byproduct, an alternative and simple parameterization of Stiefel and Grassmann manifolds is obtained.Comment: 21 page

Spatiotemporally Localized Multidimensional Solitons in Self-Induced Transparency Media

"Light bullets" are multi-dimensional solitons which are localized in both space and time. We show that such solitons exist in two- and three-dimensional self-induced-transparency media and that they are fully stable. Our approximate analytical calculation, backed and verified by direct numerical simulations, yields the multi-dimensional generalization of the one-dimensional Sine-Gordon soliton.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

From attosecond to zeptosecond coherent control of free-electron wave functions using semi-infinite light fields

Light-electron interaction in empty space is the seminal ingredient for free-electron lasers and also for controlling electron beams to dynamically investigate materials and molecules. Pushing the coherent control of free electrons by light to unexplored timescales, below the attosecond, would enable unprecedented applications in light-assisted electron quantum circuits and diagnostics at extremely small timescales, such as those governing intramolecular electronic motion and nuclear phenomena. We experimentally demonstrate attosecond coherent manipulation of the electron wave function in a transmission electron microscope, and show that it can be pushed down to the zeptosecond regime with existing technology. We make a relativistic pulsed electron beam interact in free space with an appropriately synthesized semi-infinite light field generated by two femtosecond laser pulses reflected at the surface of a mirror and delayed by fractions of the optical cycle. The amplitude and phase of the resulting coherent oscillations of the electron states in energymomentum space are mapped via momentum-resolved ultrafast electron energy-loss spectroscopy. The experimental results are in full agreement with our theoretical framework for light-electron interaction, which predicts access to the zeptosecond timescale by combining semi-infinite X-ray fields with free electrons.Comment: 22 pages, 6 figure

Sonic-Point Model of Kilohertz Quasi-Periodic Brightness Oscillations in Low-Mass X-ray Binaries

Strong, coherent, quasi-periodic brightness oscillations (QPOs) with frequencies ranging from about 300 Hz to 1200 Hz have been discovered with the Rossi X-ray Timing Explorer in the X-ray emission from some fifteen neutron stars in low-mass binary systems. Two simultaneous kilohertz QPOs differing in frequency by 250 to 350 Hertz have been detected in twelve of the fifteen sources. Here we propose a model for these QPOs. In this model the X-ray source is a neutron star with a surface magnetic field of 10^7 to 10^10 G and a spin frequency of a few hundred Hertz, accreting gas via a Keplerian disk. The frequency of the higher-frequency QPO in a kilohertz QPO pair is the Keplerian frequency at a radius near the sonic point at the inner edge of the Keplerian flow whereas the frequency of the lower-frequency QPO is approximately the difference between the Keplerian frequency at a radius near the sonic point and the stellar spin frequency. This model explains naturally many properties of the kilohertz QPOs, including their frequencies, amplitudes, and coherence. We show that if the frequency of the higher-frequency QPO in a pair is an orbital frequency, as in the sonic-point model, the frequencies of these QPOs place interesting upper bounds on the masses and radii of the neutron stars in the kilohertz QPO sources and provide new constraints on the equation of state of matter at high densities. Further observations of these QPOs may provide compelling evidence for the existence of a marginally stable orbit, confirming a key prediction of general relativity in the strong-field regime.Comment: 67 pages, including 15 figures and 5 tables; uses aas2pp4; final version to appear in the Astrophysical Journal on 1 December 199