Constraining alternative theories of gravity using pulsar timing arrays

The opening of the gravitational wave window by ground-based laser interferometers has made possible many new tests of gravity, including the first constraints on polarization. It is hoped that within the next decade pulsar timing will extend the window by making the first detections in the nano-Hertz frequency regime. Pulsar timing offers several advantages over ground-based interferometers for constraining the polarization of gravitational waves due to the many projections of the polarization pattern provided by the different lines of sight to the pulsars, and the enhanced response to longitudinal polarizations. Here we show that existing results from pulsar timing arrays can be used to place stringent limits on the energy density of longitudinal stochastic gravitational waves. Paradoxically however, we find that longitudinal modes will be very difficult to detect due to the large variance in the pulsar-pulsar correlation patterns for these modes. Existing upper limits on the power spectrum of pulsar timing residuals imply that the amplitude of vector longitudinal and scalar longitudinal modes at frequencies of 1/year are constrained: ${\cal A}_{\rm VL} < 4.1\times 10^{-16}$ and ${\cal A}_{\rm SL} < 3.7\times 10^{-17}$, while the bounds on the energy density for a scale invariant cosmological background are: $\Omega_{\rm VL}h^2 < 3.5 \times 10^{-11}$ and $\Omega_{\rm SL}h^2 < 3.2 \times 10^{-13}$.Comment: 5 pages, 4 figure

Uranium occurrences in the Horton Group of the Windsor area, Nova Scotia and the environmental implications for the Maritimes Basin

Uranium enrichment occurs at numerous localities in the basin-fill units of the Maritimes Basin, and in the adjacent basement rocks in Atlantic Canada. The exploration model applied to the sandstone-hosted occurrences is that of a uranium roll-front, similar to the deposits of Texas and the western United States. The recognition of deeply weathered granitoid rocks below the unconformity of the Horton Group on the South Mountain Batholith, however, suggests an additional genetic link to regolith-related unconformity deposits, such as the Athabasca Basin of Saskatchewan. There is no doubt that roll-front type uranium mineralization occurs in Horton Group sandstone; however, the source of the uranium within the system may be related to weathered horizons in the basement rocks beneath the Horton Group and not exclusively the result of diagenetic change in the sandstone. Uranium occurrences are numerous in the type area of the Horton Group near Windsor, Nova Scotia. The most notable occurrence is at Three Mile Plains where Saarberg Interplan Canada Ltd. drilled over 40 diamond-drill holes from 1978 to 1981. Significant uranium mineralization is stratigraphically restricted to the top of the Horton Bluff Formation and base of the Cheverie Formation near the Horton Bluff-Cheverie unconformity. The uranium mineralization can be divided into two types: (1) carbon and pyrite-related quartz sandstone type and (2) hematite arkosic sandstone type. Although this paper deals primarily with uranium and associated elements from occurrences in the Windsor area, the regional nature of the pre-Carboniferous weathering episode and the areal extent of Horton Group strata throughout eastern Canada suggests that uranium enrichment is likely more widespread than has been documented currently in the Maritimes Basin. Particular note should be taken in areas that have uranium occurrences within granitoid basement rocks adjacent to Carboniferous basin-fill. Preliminary leaching experiments of the mineralized rocks indicate that uranium and radon are easily leached from the samples and entering into the present-day environment. RÉSUMÉ L’enrichissement d’uranium survient en de nombreux endroits des unités sédimentaires du bassin des Maritimes, ainsi que dans les roches du socle adjacent au Canada atlantique. Le modèle d’exploration utilisé dans les minéralisations des grès est celui du front de minéralisation d’uranium, semblable à celui des gisements du Texas et dans l’Ouest des États-Unis. L’identification de roches granitoïdes fortement altérées sous la discordance du groupe Horton, dans la formation de batholithe South Mountain, semble toutefois suggérer la présence d’un autre lien génétique avec des gisements discordants associés au régolite, comme ce que l’on peut observer dans le bassin Athabasca, en Saskatchewan. Nul doute que la minéralisation de front d’uranium est présente dans les grès du groupe Horton. Toutefois, la provenance de l’uranium dans le système pourrait s’expliquer par des horizons météorisés dans les roches du socle sous-jacent du groupe Horton et non pas uniquement par un changement diagénétique survenu dans les grès. Les minéralisations d’uranium sont nombreuses dans la région type du groupe Horton, près de Windsor, en Nouvelle-Écosse. La minéralisation la plus notable se trouve à Three Mile Plains, où l’entreprise Saarberg Interplan Canada Ltd. a réalisé 40 trous de forage au diamant entre 1978 et 1981. La minéralisation d’uranium d’importance est délimitée au plan lithologique à la strate supérieure de la Formation de Horton Bluff et à la base de la Formation de Cheverie, à proximité de la discordance Horton Bluff-Cheverie. La minéralisation d’uranium peut se répartir en deux catégories : (1) des grès quartzeux associés au carbone et à la pyrite; et (2), des grès arkosiques ayant subi une hématisation. Bien que ce document traite pour l’essentiel de l’uranium et des éléments connexes minéralisés dans la région de Windsor, la nature régionale de la météorisation survenue avant le Carbonifère et la superficie de la lithologie du groupe Horton dans tout l’est du Canada, portent à croire que l’enrichissement d’uranium est vraisemblablement plus répandu que ce qui a été établi jusqu’ici dans le bassin des Maritimes. Il conviendrait de porter une attention particulière aux secteurs où une minéralisation d’uranium est observée dans les roches granitoïdes du socle qui jouxtent les unités sédimentaires du bassin du Carbonifère. Des essais préliminaires de lixiviation des roches minéralisées indiquent que les échantillons d’uranium et de radon sont facilement lessivés dans l’environnement actuel. [Traduit par la redaction

The work of return to work. Challenges of returning to work when you have chronic pain : a meta-ethnography

Aims To understand obstacles to returning to work, as perceived by people with chronic non-malignant pain and as perceived by employers, and to develop a conceptual model. Design Synthesis of qualitative research using meta-ethnography. Data sources Eleven bibliographic databases from inception to April 2017 supplemented by citation tracking. Review methods We used the methods of meta-ethnography. We identified concepts and conceptual categories, and developed a conceptual model and line of argument. Results We included 41 studies. We identified three core categories in the conceptual model: managing pain, managing work relationships and making workplace adjustments. All were influenced by societal expectations in relation to work, self (self-belief, self-efficacy, legitimacy, autonomy and the meaning of work for the individual), health/illness/pain representations, prereturn to work support and rehabilitation, and system factors (healthcare, workplace and social security). A mismatch of expectations between the individual with pain and the workplace contributed to a feeling of being judged and difficulties asking for help. The ability to navigate obstacles and negotiate change underpinned mastering return to work despite the pain. Where this ability was not apparent, there could be a downward spiral resulting in not working. Conclusions For people with chronic pain, and for their employers, navigating obstacles to return to work entails balancing the needs of (1) the person with chronic pain, (2) work colleagues and (3) the employing organisation. Managing pain, managing work relationships and making workplace adjustments appear to be central, but not straightforward, and require substantial effort to culminate in a successful return to work

Putative Auditory-Evoked Neurophonic Measurements Using a Novel Signal Processing Technique: A Pilot Case Study

With changes to cochlear implant candidacy and improvements in surgical technique, there is a need for accurate intraoperative assessment of low-frequency hearing thresholds during cochlear implantation. In electrocochleography, onset compound action potentials (CAPs) typically allow estimation of auditory threshold for frequencies above 1 kHz, but they are less accurate at lower frequencies. Auditory nerve neurophonic (ANN) waveforms, on the other hand, may overcome this limitation by allowing phase-locked neural activity to be tracked during a prolonged low-frequency stimulus rather than just at its onset (Henry, 1995). Lichtenhan et al. (2013) have used their auditory nerve overlapped waveform (ANOW) technique to measure these potentials from the round windows of cats and guinea pigs, and reported that in guinea pigs these potentials originate in the cochlear apex for stimuli below 70 dB SPL (Lichtenhan et al., 2014). Human intraoperative round window neurophonic measurements have been reported by Choudhury et al. (2012). We have done the same in hearing impaired awake participants, and present here the results of a pilot study in which we recorded responses evoked by 360, 525, and 725 Hz tone bursts from the cochlear promontory of one participant. We also present a modification to the existing measurement technique which halves recording time, extracting the auditory neurophonic by recording a single averaged waveform, and then subtracting from it a 180° group-delayed version of itself, rather than using alternating condensation and rarefaction sound stimuli. We cannot conclude that the waveforms we measured were purely neural responses originating from the apex of the cochlea: as with all neurophonic measurement procedures, the neural responses of interest cannot be separated from higher harmonics of the cochlear microphonic without forward masking, regardless of electrode location, stimuli or post-processing algorithm. In conclusion, the extraction of putative neurophonic waveforms can easily be incorporated into existing electrocochleographic measurement paradigms, but at this stage such measurements should be interpreted with caution

Prevalence of significant liver disease in human immunodeficiency virus-infected patients exposed to Didanosine: A cross sectional study

AIM: To identify significant liver disease [including nodular regenerative hyperplasia (NRH)] in asymptomatic Didanosine (DDI) exposed human immunodeficiency virus (HIV) positive patients. METHODS: Patients without known liver disease and with > 6 mo previous DDI use had liver stiffness assessed by transient elastography (TE). Those with alanine transaminase (ALT) above upper limit normal and/or TE > 7.65 kPa underwent ultrasound scan (U/S). Patients with: (1) abnormal U/S; or (2) elevated ALT plus TE > 7.65 kPa; or (3) TE > 9.4 kPa were offered trans-jugular liver biopsy (TJLB) with hepatic venous pressure gradient (HVPG) assessment. RESULTS: Ninety-nine patients were recruited, median age 50 years (range 31-70), 81% male and 70% men who have sex with men. Ninety-five percent with VL 9.4 kPa. Seventeen (17%) met criteria for TJLB, of whom 12 accepted. All had HVPG < 6 mmHg. Commonest histological findings were steatosis (n = 6), normal architecture (n = 4) and NRH (n = 2), giving a prevalence of previously undiagnosed NRH of 2% (95%CI: 0.55%, 7.0%). CONCLUSION: A screening strategy based on TE, liver enzymes and U/S scan found a low prevalence of previously undiagnosed NRH in DDI exposed, asymptomatic HIV positive patients. Patients were more likely to have steatosis highlighting the increased risk of multifactorial liver disease in this population

Twin pregnancy in a liver transplant recipient with HIV infection

We are not aware of a report detailing the complex obstetrical and medical management of twin pregnancy in the context of HIV infection and early post-liver transplantation period. Here we describe the successful outcome of a twin pregnancy in a 28-year-old HIV-positive female receiving antiretroviral therapy and immunosuppressive therapy who was the recipient of a liver transplant for previous drug-induced liver failure

Liver collagen proportionate area predicts decompensation in patients with recurrent hepatitis C virus cirrhosis after liver transplantation

Background and Aims: Current histological scoring systems do not subclassify cirrhosis. Computer-assisted digital image analysis (DIA) of Sirius Red-stained sections measures fibrosis morphologically producing a fibrosis ratio (collagen proportionate area [CPA]). CPA could have prognostic value within a disease stage, such as cirrhosis. The aim of the present study was to evaluate CPA in patients with recurrent hepatitis C virus (HCV) allograft cirrhosis and assess its relationship with hepatic venous pressure gradient (HVPG). Methods: In 121 consecutively-transplanted HCV patients with HVPG, measured contemporaneously with transjugular liver biopsies, 65 had Ishak stage 5 or 6 disease (43 with HVPG measurement). Biopsies were stained with Sirius Red for DIA, and the collagen content was expressed as a CPA. In three cases, a tissue for Sirius Red staining was not obtained, and the patients were excluded. Results: Sixty-two patients were analyzed. The median HVPG was 8mmHg (interquartile range [IQR]: 5-10). Portal hypertension (HVPG ≥6<10mmHg) was present in 30 (69.8%), and HVPG ≥10mmHg in 13 (30.2%). The median CPA was 16% (IQR 10.75-23.25). Median Child-Pugh score and HVPG were not significantly different between Ishak fibrosis stage 5 or 6, whereas CPA was statistically different: 13% in stage 5 (IQR 8.3-12.4) versus 23% in stage 6 (IQR 17-33.7, P<0.001). In the multivariate analysis, CPA was the only variable significantly associated with clinically-significant portal hypertension (HVPG ≥10mmHg, odds ratio: 1.085, confidence interval: 1.004-1.172, P=0.040). A CPA of 14% was the best cut-off value for clinically-significant portal hypertension (CSPH) and liver decompensation, which occurred in 24 patients. Event-free survival was significantly shorter in patients with CSPH or with a CPA value ≥14%, or with a combination of both. Conclusion: In Ishak stages 5 and 6, CPA correlated with HVPG, but had a wider range of values, suggesting a greater sensitivity for distinguishing "early" from "late" severe fibrosis/cirrhosis. CPA was a unique, independent predictor of HVPG ≥10mmHg. CPA can be used to subclassify cirrhosis and for prognostic stratification. © 2012 Journal of Gastroenterology and Hepatology Foundation and Blackwell Publishing Asia Pty Ltd

Endoscopy management algorithms: role of cyanoacrylate glue injection and self-expanding metal stents in acute variceal haemorrhage

Mortality from acute variceal bleeding (AVB) has improved markedly over the last 2–3 decades due to increased specialisation and standardisation of medical and endoscopic practice culminating in the production of consensus guidance based on expert opinion. Nonetheless, despite greater exposure, training and endoscopic practices, 30-day mortality still remains high at around 30%. This is a reflection of the high morbidity with liver disease, and limited endoscopic experience and/or endoscopic techniques used by the majority of general endoscopists. Clinical necessity defines our drive for further endoscopic innovation to improve ‘best practice’ and, therefore, clinical outcomes accordingly. Sclerotherpy, variceal band ligation and/or rescue balloon tamponade have been entrenched in most treatment algorithms over the decades. However, in recent years and albeit limited to specialised liver centres, cyanoacrylate glue injection therapy (for oesophageal and gastric varices), and the placement of a self-expanding metallic stent for oesophageal varices have begun to offer improved endoscopic care in experienced hands. Yet even in specialised centres, their application is sporadic and operator dependent. Here, we discuss the evidence of these newer endoscopic approaches, and hope to propose their inclusion in endoscopic therapy algorithms for ‘best practice’ management of AVB in all appropriately supported endoscopy units