Long-lived selective spin echoes in dipolar solids under periodic and aperiodic pi-pulse trains

The application of Carr-Purcell-Meiboom-Gill (CPMG) $\pi-$trains for dynamically decoupling a system from its environment has been extensively studied in a variety of physical systems. When applied to dipolar solids, recent experiments have demonstrated that CPMG pulse trains can generate long-lived spin echoes. While there still remains some controversy as to the origins of these long-lived spin echoes under the CPMG sequence, there is a general agreement that pulse errors during the $\pi-$pulses are a necessary requirement. In this work, we develop a theory to describe the spin dynamics in dipolar coupled spin-1/2 system under a CPMG($\phi_{1},\phi_{2}$) pulse train, where $\phi_{1}$ and $\phi_{2}$ are the phases of the $\pi-$pulses. From our theoretical framework, the propagator for the CPMG($\phi_{1},\phi_{2}$) pulse train is equivalent to an effective ``pulsed'' spin-locking of single-quantum coherences with phase $\pm\frac{\phi_{2}-3\phi_{1}}{2}$, which generates a periodic quasiequilibrium that corresponds to the long-lived echoes. Numerical simulations, along with experiments on both magnetically dilute, random spin networks found in C$_{60}$ and C$_{70}$ and in non-dilute spin systems found in adamantane and ferrocene, were performed and confirm the predictions from the proposed theory.Comment: 25 pages, 12 figures, submitted to Physical Review

The Changing Narratives of Death, Dying, and HIV in the United Kingdom

Death and infection were closely linked from the start of the HIV epidemic, until successful treatments became available. The initial impact of mostly young, gay men dying from HIV was powerful in shaping UK responses. Neoliberal discourses developed at the same time, particularly focusing on how citizens (rather than the state) should take responsibility to improve health. Subsequently “successful ageing” became an allied discourse, further marginalising death discussions. Our study reflected on a broad range of meanings around death within the historical UK epidemic, to examine how dying narratives shape contemporary HIV experiences. Fifty-one participants including people living with HIV, professionals, and activists were recruited for semistructured interviews. Assuming a symbolic interactionist framework, analysis highlighted how HIV deaths were initially experienced as not only traumatic but also energizing, leading to creativity. With effective antiretrovirals, dying changed shape (e.g., loss of death literacy), and better integration of palliative care was recommended

Gram-Negative Bacteria and Sepsis

Today’s medical world encompasses an environment in which gram-negative bacteria that once were defeated with common antibiotics, have now become resistant. Gram-negative bacteria like Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter, and Acinetobacter are pathogens that are an emerging threat causing sepsis due to multidrug-resistance (Pop-Vicas & Opal, 2014, p.189). The multidrug-resistance mechanisms of gram-negative bacteria coupled with a patient population commonly seen in hospital settings, that consist of immunocompromised adults due to advancing age, comorbidities (e.g. AIDS, history of transplants, diabetes, and chemotherapy), and immunotherapies, create an environment for advanced infection or sepsis to take place. Complications of multidrug-resistant gram-negative bacteria can cause infection and ultimately sepsis in the host. Gram-negative bacteria with multidrug-resistance has caused a rise in hospital admissions across The United States. The Centers for Disease Control and Prevention (2014), reported that between the years of 2000 and 2008 the number of patients admitted with sepsis increased from 621,000 to 1,141,000 respectively. This increase in hospital admissions has resulted in sepsis being the most expensive medical condition since 2011 with a cumulative cost of over $20.3 billion (Chong et al., 2015, p. 111). The topic of gram-negative bacteria and sepsis was chosen due to the medical challenge presented to healthcare providers and the high mortality rates associated with gram-negative bacteria. Traditional management and treatment of sepsis resulting from gram-negative bacteria is no longer effective and healthcare providers are having to update and modify current sepsis protocols to fight the infection

Ageing with HIV

Applying Fraser’s inequalities framework to our UK-based HIV and Later Life (HALL) study, we show that, for the growing population of older people living with HIV (PLWH), HIV intersects with ethnicity, sex, sexuality, stigma, and ageism to produce bivalent identities. These shape their experience of ageing with HIV and intersect with economic factors, the social status order, and statutory policy to subject them to socioeconomic and cultural injustices only roughly captured by Fraser’s three domains of inequality. Under recognition, the stigmatization of HIV and its exacerbation by normative ageist expectations threaten social relationships. Under resources, older PLWH’s disproportionate financial disadvantage, linked to interrupted work histories, uncertain migration status, and recent changes to benefits on which PLWH are disproportionately reliant and whose new criteria disadvantage them, make access to support from others living with HIV and from HIV organizations even more essential for mental health and wellbeing. Finally, under representation, stigma and homophobia in care settings may undermine the quality of long-term care, and defunding of HIV organizations and welfare benefit changes via neo-liberal policies and austerity measures create political disenfranchisement and barriers to social participation. Thus, Fraser’s clear-cut domains imperfectly capture factors undermining underlying causes of older PLWH’s disadvantage: HIV-specific supports (resources) established to compensate for difficulties emanating from Fraser’s recognition and resources domains are increasingly threatened by agents operating within Fraser’s representation domain. Our conclusion considers other sources of older PLWH’s underrepresentation: their waning participation in activism and advocacy on their own behalf, and inadequate attention by non-HIV organizations

Taurek, numbers and probabilities

In his paper, “Should the Numbers Count?" John Taurek imagines that we are in a position such that we can either save a group of five people, or we can save one individual, David. We cannot save David and the five. This is because they each require a life-saving drug. However, David needs all of the drug if he is to survive, while the other five need only a fifth each.Typically, people have argued as if there was a choice to be made: either numbers matter, in which case we should save the greater number, or numbers don't matter, but rather there is moral value in giving each person an equal chance of survival, and therefore we should toss a coin. My claim is that we do not have to make a choice in this way. Rather, numbers do matter, but it doesn't follow that we should always save the greater number. And likewise, there is moral value in giving each person an equal chance of survival, but it doesn't follow that we should always toss a coin.In addition, I argue that a similar approach can be applied to situations in which we can save one person or another, but the chances of success are different

The interaction of ions with nonpolar neutrals: The collision broadening of ion cyclotron resonance lines of ions in hydrogen and methane

The motion of ions in an ion cyclotron resonance cell is considered, and measurements of ion cyclotron resonance linewidths are described. The connection between cyclotron resonance linewidths and kinetic parameters is developed. Mobilities and collision frequencies of CH5 + , C2H5 + , C3H7 + , C4H9 + , and Na + in methane and H + , H3 + , H30 + , CH5 + , C2H5 + , C3H7 + , and Na + in hydrogen are determined from the linewidth measurements. Resulting mobilities of H + , H3 + , and Na + in H2 are found to agree well with drift tube measurements, in contrast to previous cyclotron resonance linewidth determinations. The mobilities are interpreted in terms of three model ion molecule interaction potentials. The mobilities are found to be in general consistent with both a three term 12–6–4 potential and an acentric potential but not with the simple polarization potential. Potential parameters consistent with binding energies from the literature and the present mobility measurements are reported for H3 + –H2, CH5 + –CH4, and C2H5 + –CH4

'I was so done in that I just recognized it very plainly, "You need to do something"': Men's narratives of struggle, distress and turning to meditation

Traditional masculinities can mean men are unable or unwilling to deal constructively with distress. However, researchers increasingly acknowledge that men and masculinities (including hegemonic styles) are diverse. Moreover, men can positively manage their well-being, although little research explores how they do so. Uniquely, our study sought to find men who report finding ways to care for themselves to examine narratives about how such self-care originated. We aimed to do this by exploring issues underpinning men’s journeys towards meditation, focusing on implications for well-being. In-depth interviews were conducted in 2009 with 30 meditators, selected using principles of maximum variation sampling, and analysed with a modified ‘constant comparison’ approach. Men’s journeys towards meditation were fraught with difficulties. Men described crossing a threshold from boyhood into ‘manhood’ where they encountered traditional forms of masculinity (e.g. stoicism), and most described subsequent strategies to disconnect from emotions. While men eventually found ways to engage more constructively with their emotions and well-being, this article explores the struggle and distress of their journeys

How older people living with HIV narrate their quality of life: Tensions with quantitative approaches to quality-of-life research

This article draws on life-history interviews with older (aged 50+) people living with HIV in England to uncover the interpretive practices in which they engaged as they evaluated their own quality of life (QoL). Our paper highlights the distinctive insights that biographical and narrative approaches can bring to QoL research. While accounts of subjectively ‘poor’ QoL were relatively straightforward and unequivocally phrased, accounts of subjectively ‘good’ and ‘OK’ QoL were produced using complex interpretive and evaluative practices. These practices involved biographical reflection and contextualization, with participants weighing up and comparing their current lives’ ‘pros’ and ‘cons’, their own lives with the lives of others, and their present lives with lives they had imagined having at the time of interview. Thus, ‘good’ and ‘OK’ QoL were constructed using practical, relational, and interpretive work – features of QoL analytically unavailable in quantitative data gathered through standardised measures (including our own survey data collected from these same participants). Our findings underscore the uneasy fit between QoL’s quantitative measurement and its subjective understandings and evaluations, on the one hand, and the interpretive work that goes into achieving these understandings and evaluations, on the other

Amine reactivity with charged sulfuric acid clusters

The distribution of charged species produced by electrospray of an ammonium sulfate solution in both positive and negative polarities is examined using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Positively-charged ammonium bisulfate cluster composition differs significantly from negatively-charged cluster composition. For positively-charged clusters all sulfuric acid is neutralized to bisulfate, whereas for negatively-charged clusters the degree of sulfuric acid neutralization is cluster size-dependent. With increasing cluster size (and, therefore, a decreasing role of charge), both positively- and negatively-charged cluster compositions converge toward ammonium bisulfate. The reactivity of negatively-charged sulfuric acid-ammonia clusters with dimethylamine and ammonia is also investigated by FTICR-MS. Two series of negatively-charged clusters are investigated: [(HSO<sub>4</sub>)(H<sub>2</sub>SO<sub>4</sub>)<sub>x</sub>]<sup>−</sup> and [(NH<sub>4</sub>)<sub>x</sub>(HSO<sub>4</sub>)<sub>x+1</sub>(H<sub>2</sub>SO<sub>4</sub>)<sub>3</sub>]<sup>−</sup>. Dimethylamine substitution for ammonia in [(NH<sub>4</sub>)<sub> x</sub>(HSO<sub>4</sub>)<sub> x+1</sub>(H<sub>2</sub>SO<sub>4</sub>)<sub>3</sub>]<sup>−</sup> clusters is nearly collision-limited, and subsequent addition of dimethylamine to neutralize H<sub>2</sub>SO<sub>4</sub> to bisulfate is within one order of magnitude of the substitution rate. Dimethylamine addition to [(HSO<sub>4</sub>) (H<sub>2</sub>SO<sub>4</sub>)<sub> x</sub>]<sup>−</sup> clusters is either not observed or very slow. The results of this study indicate that amine chemistry will be evident and important only in large ambient negative ions (><i>m/z</i> 400), whereas amine chemistry may be evident in small ambient positive ions. Addition of ammonia to unneutralized clusters occurs at a rate that is ~2–3 orders of magnitude slower than incorporation of dimethylamine either by substitution or addition. Therefore, in locations where amine levels are within a few orders of magnitude of ammonia levels, amine chemistry may compete favorably with ammonia chemistry