Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries.

Reliable neutron star mass measurements are key to determining the equation of state of cold nuclear matter, but such measurements are rare. Black widows and redbacks are compact binaries consisting of millisecond pulsars and semi-degenerate companion stars. Spectroscopy of the optically bright companions can determine their radial velocities, providing inclination-dependent pulsar mass estimates. Although inclinations can be inferred from subtle features in optical light curves, such estimates may be systematically biased due to incomplete heating models and poorly understood variability. Using data from the Fermi Large Area Telescope, we have searched for gamma-ray eclipses from 49 spider systems, discovering significant eclipses in 7 systems, including the prototypical black widow PSR B1957+20. Gamma-ray eclipses require direct occultation of the pulsar by the companion, and so the detection, or significant exclusion, of a gamma-ray eclipse strictly limits the binary inclination angle, providing new robust, model-independent pulsar mass constraints. For PSR B1957+20, the eclipse implies a much lighter pulsar (1.81 ± 0.07 solar masses) than inferred from optical light curve modelling.

A dense ring of the trans-Neptunian object Quaoar outside its Roche limit.

Planetary rings are observed not only around giant planets1, but also around small bodies such as the Centaur Chariklo2 and the dwarf planet Haumea3. Up to now, all known dense rings were located close enough to their parent bodies, being inside the Roche limit, where tidal forces prevent material with reasonable densities from aggregating into a satellite. Here we report observations of an inhomogeneous ring around the trans-Neptunian body (50000) Quaoar. This trans-Neptunian object has an estimated radius4 of 555 km and possesses a roughly 80-km satellite5 (Weywot) that orbits at 24 Quaoar radii6,7. The detected ring orbits at 7.4 radii from the central body, which is well outside Quaoar's classical Roche limit, thus indicating that this limit does not always determine where ring material can survive. Our local collisional simulations show that elastic collisions, based on laboratory experiments8, can maintain a ring far away from the body. Moreover, Quaoar's ring orbits close to the 1/3 spin-orbit resonance9 with Quaoar, a property shared by Chariklo's2,10,11 and Haumea's3 rings, suggesting that this resonance plays a key role in ring confinement for small bodies.

A dense 0.1-solar-mass star in a 51-minute-orbital-period eclipsing binary.

Of more than a thousand known cataclysmic variables (CVs), where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes1-9. One way to achieve these short periods requires the donor star to have undergone substantial nuclear evolution before interacting with the white dwarf10-14, and it is expected that these objects will transition to helium accretion. These transitional CVs have been proposed as progenitors of helium CVs13-18. However, no known transitional CV is expected to reach an orbital period short enough to account for most of the helium CV population, leaving the role of this evolutionary pathway unclear. Here we report observations of ZTF J1813+4251, a 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater owing to its helium-rich composition, accreting onto a white dwarf. Phase-resolved spectra, multi-band light curves and the broadband spectral energy distribution allow us to obtain precise and robust constraints on the masses, radii and temperatures of both components. Evolutionary modelling shows that ZTF J1813+4251 is destined to become a helium CV binary, reaching an orbital period under 20 minutes, rendering ZTF J1813+4251 a previously missing link between helium CV binaries and hydrogen-rich CVs.

A 62-minute orbital period black widow binary in a wide hierarchical triple.

Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original 'black widow', the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)1, high-energy emission originating from the pulsar2 is irradiating and may eventually destroy3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars4, allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models5, falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics6 and binary evolution.

Fibrin glue inhibits migration of ocular surface epithelial cells.

PurposeFibrin glue has been used successfully in numerous ophthalmic surgical procedures. Recently, fibrin glue has been used in limbal stem cell transplantation to reduce both operative time and to negate the need for sutures. The aim of this study was to determine the effects of fibrin glue on epithelial cell migration in vitro.MethodsCorneoscleral rims were split to retain the epithelial layer, Bowman's layer, and anterior stroma. Rims were cut into eight equal-sized pieces and were placed directly on culture plates or affixed with fibrin glue. Rims were maintained in culture for 25 days and epithelial cell growth was monitored. Cells were photographed to measure area or growth and immunofluorescence staining of explants for fibrin was performed.ResultsExplants that were glued demonstrated significantly delayed epithelial cell growth and migration as compared with explants without glue. By day 16, all fibrin glue had dissolved and coincided with onset of cell growth from glued explants. Cell growth commenced between days 3 and 4 for control explants without glue and around days 14-16 for explants with fibrin glue.ConclusionsFibrin glue delays epithelial cell migration by acting as a physical barrier and can potentially interfere with explant-derived limbal epithelial cell migration on to the corneal surface. We propose that glue should be used to attach the conjunctival frill of the limbal explant but care should be taken to ensure that the glue does not wrap around the explant if used to secure the explant as well. Strategic use of glue, to attach the recessed conjunctiva, can be advantageous in delaying conjunctival cell migration and reducing the need for sequential sector conjunctival epitheliectomy.

A radio-pulsing white dwarf binary star.

White dwarfs are compact stars, similar in size to Earth but approximately 200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf/cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56-hour period close binary, pulsing in brightness on a period of 1.97 minutes. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 seconds, and they are also detectable at radio frequencies. They reflect the spin of a magnetic white dwarf, which we find to be slowing down on a 107-year timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they mainly originate from the cool star. AR Sco's broadband spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation.

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420 ± 60 km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1σ) and 1,502 ± 45 km, implying a V-band geometric albedo p(V) = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12 nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm(-3) is inferred from the data.

Systemic mastocytosis presenting as osteoporosis--a case report.

Mastocytosis is a clonal disorder of the mast cell and its precursor cells, and is characterised by proliferation and accumulation of mast cells within various organs, most commonly the skin. Systemic mastocytosis is a rare but well-recognised cause of secondary osteoporosis, accounting for about 1.25% of cases. The pathophysiological mechanism is probably multifactorial, including increased osteoclastic activity, and a direct effect of mast cell mediators like histamine, heparin, tryptase and cytokines. Here, we report the case of a middle-aged male patient with osteoporotic vertebral fractures as a rare presenting manifestation of systemic mastocytosis. In summary, systemic mastocytosis, although rare, should be considered as a cause in patients with idiopathic osteoporosis.

A brown dwarf mass donor in an accreting binary.

A long-standing and unverified prediction of binary star evolution theory is the existence of a population of white dwarfs accreting from substellar donor stars. Such systems ought to be common, but the difficulty of finding them, combined with the challenge of detecting the donor against the light from accretion, means that no donor star to date has a measured mass below the hydrogen burning limit. We applied a technique that allowed us to reliably measure the mass of the unseen donor star in eclipsing systems. We were able to identify a brown dwarf donor star, with a mass of 0.052 +/- 0.002 solar mass. The relatively high mass of the donor star for its orbital period suggests that current evolutionary models may underestimate the radii of brown dwarfs.

Influence of endogenous and exogenous orientations of attention on inhibition of return in a cross-modal target-target aiming task.

The authors conducted 2 experiments in which participants (N = 16 in each) executed successive unimanual aiming movements to target locations that were indicated by the onset of either an auditory or a visual stimulus. In Experiment 1 (exogenous orientation), inhibition of return (IOR) effects were observed, with reliable reaction time (RT) costs associated with movements returning to the same target and a trend toward larger IOR effects in left than in right space. There was no influence of stimulus modality on the magnitude of IOR. IOR was also observed in Experiment 2 (endogenous orientation), except the influence of stimulus modality reliably mediated those effect. In that case, IOR was evident only when the previous modality was visual and the current modality was auditory. Together, the results of those 2 experiments suggest that in situations in which 2 paired movements constitute the response criteria, IOR is both supramodal and lateralized to contralateral space.

Comparison of DNA damage and repair following radiation challenge in buccal cells and lymphocytes using single-cell gel electrophoresis.

PURPOSE: To develop a reproducible single-cell gel electrophoresis assay for DNA damage and repair in buccal mucosa and sublingual exfoliated cells. MATERIALS AND METHODS: Buccal mucosa and sublingual cells and lymphocytes from six individuals (three males, three females, aged 34-45 years) were challenged with increasing doses of gamma-rays. DNA strand breaks and DNA repair were measured using the single-cell gel electrophoresis assay. RESULTS: Baseline DNA strand breaks were significantly greater in buccal mucosa and sublingual cells compared with lymphocytes. Buccal mucosa and sublingual cells did not differ from each other with respect to induction of DNA strand breaks by 2 or 4 Gy gamma-rays. However, they showed a smaller increase in gamma-ray-induced DNA strand breaks compared with lymphocytes (32-53% less than lymphocytes; ANOVA p<0.0001). Unlike lymphocytes, which repaired 83% of DNA strand breaks, buccal mucosa and sublingual cells exhibited only a minimal capacity for DNA repair (approximately 0-14% of the level in lymphocytes). CONCLUSIONS: Buccal mucosa and sublingual cells exhibit an apparent resistance to the expression of radiation-induced DNA strand breaks in vitro and an apparent lack of DNA strand break repair in the single-cell gel electrophoresis assay.

Promoter hypermethylation of MGMT, CDH1, RAR-beta and SYK tumour suppressor genes in granulosa cell tumours (GCTs) of ovarian origin.

Ovarian carcinoma (OC) is a leading cause of death among women throughout the world. A number of cancer-associated genes have been shown to be inactivated by hypermethylation of CpG islands during tumorigenesis. We tested the hypothesis that methylation status of MGMT, CDH1, RAR-beta and SYK could be important in the ovarian tumorigenic process and can lead to the gene(s) inactivation. Therefore, we assessed the promoter hypermethylation of MGMT, CDH1, RAR-beta and SYK in 43 ovarian granulosa cell tumours (GCTs) (adult type) using methylation-specific PCR. These tumours are relatively rare, accounting for approximately 3% of all ovarian cancers. Hypermethylation of MGMT (in 14 tumours), CDH1 (in nine tumours), RAR-beta (in eight tumours) and SYK (in seven tumours) have been found. Selective loss of RAR-beta and RAR-beta2 mRNA has been found in seven patients, while that of MGMT and SYK in three patients who also show aberrant methylation in promoter region of RAR-beta in addition to MGMT, SYK and CDH1 genes. Promoter CpG hypermethylation may be an alternative to mutation(s) to inactivate tumour suppressor genes such as MGMT, CDH1, RAR-beta and SYK, and this can also be an early event in the pathogenesis of OCs. Moreover, hypermethylation of the MGMT and CDH1, MGMT and RAR-beta and CDH1 and RAR-beta promoters occurred concordantly (P< 0.001, 0.0421 and 0.0005 respectively; Fischer's exact test). In addition to this, monosomy 22 and trisomy 14 have also been found in 10 tumours. It is clear from the results that hypermethylation of the promoter region of these tumour suppressor genes, monosomy 22 and trisomy 14, may be critical steps in the tumorigenesis, which consequently play a permissive role for tumour aggressiveness. All these events might play an important role in the early clinical diagnosis of the disease. Our results, therefore, suggest a potential role for epigenetic modification of these critical tumour suppressor genes in pathways relevant to the transformation and differentiation of rare type of ovarian cancer (GCTs).

The effect of DXA scanning on clinical decision making by general practitioners: a randomized, prospective trial of direct access versus referral to a hospital consultant.

The objective of the study was to assess the impact of direct access DXA scanning (DADS) upon GPs' management decisions in patients considered to be at risk of osteoporosis. It was designed as a randomized, prospective, parallel group trial, set within the primary care environment and a university teaching hospital. The participants were 330 patients aged 31 to 89 years from 18 general practices in Edinburgh. Patients were randomized to either DADS or to the current system of specialist referral (controls). The primary outcome measure was frequency of change of management after DXA scanning. Secondary outcome measures were: change in health status, adherence to therapy, clinical events and resource use at one-year follow-up. The primary outcome was that 60% each of DADS patients (98/165) and controls (99/165) had changes in management following DXA scanning. In 30% of patients (12/41) in whom GPs had proposed changing management even in the absence of a scan, different therapy was chosen after the scan (no difference between DADS and control groups). There was an improvement in health utility (p =0.014 for both groups combined), differing slightly between the two groups even after age correction (p =0.014). 68% of the DADS group and 70% of controls were adherent to therapy after one year. In terms of clinical events, at one year there was one major adverse event (control group patient), 5 new fractures in the DADS group and 3 in controls - there were no hip fractures in this study. With regard to resource use, there were 24 referrals to hospital specialist after DXA scanning among the DADS group, vs 12 among controls (p < 0.05). The total number of visits to health professionals was 525 in DADS and 585 in controls (p=ns); mean waiting time from randomization to receipt of report/clinic letter was 4 weeks for DADS vs 13 weeks for controls( p < 0.0001). In conclusion, DXA scanning resulted in management change in at least 60% of cases. Direct access does not result in a clinical outcome significantly different from a consultant led service, and is more economically efficient than the current model of hospital referral.

Chromosome aberrations and sister chromatid exchange studies in patients with prostate cancer: possible evidence of chromosome instability.

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 24 patients with prostate cancer. Of these, eight belong to stage B, six to stage C/e, three to C/sv, two to Do, and the remaining five to DI stage of carcinoma. Simultaneously, sister chromatid exchanges (SCEs) were also analyzed in the peripheral blood lymphocytes of these patients, along with those of 40 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with prostate cancer (7.32%) than in age-matched controls (2.92%). A large number of chromosome aberrations in lymphocytes of these patients, which are generally constitutional in nature, have also been detected. In stage-B patients, the frequency of cytogenetically abnormal cells is comparatively low with regard to the number of cells scanned, and these abnormalities are generally confined only to single chromosome (except in one metaphase in patient 1, who was diagnosed with bladder carcinoma in addition to cancer of the prostate). Sister chromatid exchanges (SCEs) were also analyzed in the patients and age-matched control subjects. The mean SCE frequencies were 9.24 +/- 0.62 (n = 1356) per metaphase and 0.203 per chromosome in patients, whereas in control subjects the frequencies were 5.94 +/- 0.25 (n = 4000) per metaphase and 0.129 per chromosome. The SCE frequency in cancer patients was statistically significant (p < 0.001). Our results indicate that the patients with prostate cancer show a degree of chromosomal instability that might be related to a predisposition to neoplasia.

Genotoxic potential of estrogens.

A genotoxicity evaluation of three commonly used estrogens-ethinyl estradiol, cyclotriol and cyclodiol was undertaken using short-term in vitro and in vivo assays. None of the drugs caused significantly increased or decreased number of His+ mutants to appear in the Ames Salmonella assay, either with or without S9 mix or in a modified host-mediated version of this assay. However, the clastogenic potential of these drugs became evident from the increased number or chromosome aberrations and sister chromatid exchanges (SCEs) induced by these drugs in human lymphocyte cultures both in the presence and absence of S9 mix. Increased frequencies of micronuclei and of sister chromatid exchanges in mice confirmed their clastogenic potential.

Choromosome instabililty and sister chromatid exchange (SCE) studies in patients with carcinoma of cervix uteri.

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 14 patients with carcinoma of the cervix uteri. Simultaneously, sister chromatid exchange (SCE) was also analyzed in the peripheral blood lymphocytes of these patients, along with those of 20 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with carcinoma of the cervix uteri (7.85%) than in the age-matched controls (3.35%). A large number of chromosome aberrations in lymphocytes of these patients have also been detected. Sister chromatid exchange (SCE) was also analyzed in lymphocytes of 14 patients with carcinoma of the cervix uteri and 20 age-matched control subjects. The mean SCE frequencies were 9.44 +/- 0.34 (n = 637) and 6.09 +/- 0.24 (n = 900) per metaphase in patients and controls, respectively. The increase of SCE frequency in cancer patients was statistically significant (p < 0.001), but not seen in controls. Our results suggest that patients with carcinoma of the cervix uteri show a degree of chromosomal instability that might be related to a predisposition to neoplasia.