The suppression of star formation by powerful active galactic nuclei.

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 10(11) solar masses.

The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 µm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, M(min), such that log(10)[M(min)/M(⊙)] = 11.5(+0.7)(-0.2) at 350 µm, where M(⊙) is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation.

Warm water vapour in the sooty outflow from a luminous carbon star.

The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star, grain surface reactions, and photochemistry in the outer circumstellar envelope. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite. This includes some high-excitation lines with energies corresponding to approximately 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances are much higher than hitherto predicted.

Parity violation constraints using cosmic microwave background polarization spectra from 2006 and 2007 observations by the QUaD polarimeter.

We constrain parity-violating interactions to the surface of last scattering using spectra from the QUaD experiment's second and third seasons of observations by searching for a possible systematic rotation of the polarization directions of cosmic microwave background photons. We measure the rotation angle due to such a possible "cosmological birefringence" to be 0.55 degrees +/-0.82 degrees (random) +/-0.5 degrees (systematic) using QUaD's 100 and 150 GHz temperature-curl and gradient-curl spectra over the spectra over the multipole range 200

Assessment of the reliability of high-intensity quadriceps femoris muscle fatigue.

OBJECTIVE: The purpose of this study was to evaluate test-retest reliability of two different measures of isokinetic quadriceps muscle fatigue. METHODS: Subjects for this study included 16 healthy, college age volunteers. Each subject performed 30 maximal, concentric repetitions on the Biodex System II Isokinetic Dynamometer at a preset angular velocity of 180 degrees.s(-1) for both the dominant and nondominant legs. Quadriceps work was evaluated between an angular range of 10 degrees and 60 degrees of flexion for each repetition. Quadriceps muscle fatigue was calculated through a fatigue index (work performed last 5 repetitions/work performed first five repetitions x 100) and the linear slope (beta) across the 30 repetitions. The subjects participated in two test sessions separated by one to two weeks. Intraclass correlation coefficients (ICC) and standard errors of measurements (SEM) were calculated for each fatigue measure on both legs. RESULTS: The findings demonstrated moderate to high ICCs for the nondominant leg (ICC = 0.78--0.92) and high ICCs for the slope and y-intercept for the dominant leg (ICC = 0.82 and 0.89, respectively). The fatigue index for the dominant leg was found to be low (ICC = 0.26). CONCLUSIONS: The findings of this study suggest that the quantification of muscle fatigue during high-intensity, short-term exercise is more reliably described by the slope, which is related to the magnitude of force output.

Quadriceps activation and perceived exertion during a high intensity, steady state contraction to failure.

The ability to sustain a high-intensity, steady-state muscle contraction may have differential effects on neuromuscular activation and perceived exertion. The purpose of this study was to examine changes in neuromuscular activation and perceived exertion at a near-maximal steady-state contraction of the quadriceps in healthy men. Seventeen healthy, college-aged male volunteers were studied during isometric contractions equivalent to 80% of the maximum voluntary contraction (MVC). Perceived exertion was measured with a modified category-ratio scale (CR-10). The CR-10 scale was anchored with one high anchor at 100% MVC and one low anchor at 10% MVC. Subjects then performed an 80% MVC for as long as they could sustain it. Subjects were asked to rate the feelings in their quadriceps every 5 s during the contraction. The results demonstrated significant increases in neuromuscular activation of the vastus medialis and vastus lateralis muscles (P < 0.05) during the 80% MVC, but there were no significant muscle by time interactions. The results also demonstrated a significant increase (P < 0.05) in perceived exertion during the 80% MVC. Neuromuscular activation of both muscles, and perceived exertion, were found to increase in linear (P < 0.05) and quadratic (P < 0.05) trends. Alterations in motor unit discharge properties or impairments in muscle fiber membrane excitability may account for nonlinear increases in vastii muscle activation and perceived exertion.

Knee joint laxity and neuromuscular characteristics of male and female soccer and basketball players.

Anterior cruciate ligament injuries are occurring at a higher rate in female athletes compared with their male counterparts. Research in the area of anterior cruciate ligament injury has increasingly focused on the role of joint proprioception and muscle activity in promoting knee joint stability. We measured knee joint laxity, joint kinesthesia, lower extremity balance, the amount of time required to generate peak torque of the knee flexor and extensor musculature, and electromyographically assessed muscle activity in 34 healthy, collegiate-level athletes (average age, 19.6 +/- 1.5 years) who played soccer or basketball or both. Independent t-tests were used to determine significant sex differences. Results revealed that women inherently possess significantly greater knee joint laxity values, demonstrate a significantly longer time to detect the knee joint motion moving into extension, possess significantly superior single-legged balance ability, and produce significantly greater electromyographic peak amplitude and area of the lateral hamstring muscle subsequent to landing a jump. The excessive joint laxity of women appears to contribute to diminished joint proprioception, rendering the knee less sensitive to potentially damaging forces and possibly at risk for injury. Unable to rely on ligamentous structures, healthy female athletes appear to have adopted compensatory mechanisms of increased hamstring activity to achieve functional joint stabilization.

The effects of rest interval on quadriceps torque and perceived exertion in healthy males.

BACKGROUND: The ability to generate maximal muscular force is dependent upon time mediated mechanisms of fatigue. Interset rest interval length may not only affect force production but may also manifest changes in ratings of perceived exertion (RPE). The purpose of this study was to examine the effects of rest interval on quadriceps torque and RPE during multiple sets of resisted knee extensions. METHODS: 14 healthy male volunteers were assessed for concentric isokinetic quadriceps peak torque, total work, and average power on the Biodex System II Isokinetic Dynamometer at a preset angular velocity of 180 deg.sec-1. Perceived exertion was measured with a modified category-ratio scale (CR-10). Under isometric conditions the perceptual range was anchored with one high and two low anchors. Subjects were randomly assigned to one of two groups: short rest interval (Group 1, 40 sec) and long rest interval (Group 2, 160 sec). All subjects performed 4 sets of 20 maximal isokinetic contractions with an inter-set rest interval that corresponded to their group assignment. Following the completion of each set subjects were asked to assign a rating out of 10 to the feelings in their quadriceps by visually observing a chart of the CR-10 scale. RESULTS: The results demonstrated a significantly greater decline in quadriceps peak torque (p < 0.05), total work (p < 0.05), and average power (p < 0.05) by Group 1 as compared to Group 2. Changes in RPE across the 4 sets of exercise did not show a significant difference between the 2 groups. CONCLUSIONS: The generation of quadriceps torque is a function of rest interval length, whereas perceived exertion appears to be unaffected.

Infrared variability of the BL lacertae object OJ287 since its outburst in 1983.

In early 1983, OJ287 was seen to undergo an outburst in its optical and infrared emission1. Since then optical monitoring studies2-4 have shown a general decline in the source brightness, with considerable fluctuations. We have monitored the near-infrared emission since the outburst. The fluxes have fluctuated considerably, with the lowest recordings being an order of magnitude less than those measured during the outburst. We have found an excellent correlation between infrared flux and spectral index; as the source gets fainter the spectrum gets steeper, and vice versa. We interpret this in terms of outbursts being due to injection or reacceleration of electrons with a constant energy index which subsequently steepens as the electrons are affected by radiation losses.