Gas hydrates are ice-like solids, in which guest molecules or atoms are trapped inside cages formed within a crystalline host framework (clathrate) of hydrogen-bonded water molecules. They are ...naturally present in large quantities on the deep ocean floor and as permafrost, can form in and block gas pipelines, and are thought to occur widely on Earth and beyond. A natural point of reference for this large and ubiquitous family of inclusion compounds is the empty hydrate lattice, which is usually regarded as experimentally inaccessible because the guest species stabilize the host framework. However, it has been suggested that sufficiently small guests may be removed to leave behind metastable empty clathrates, and guest-free Si- and Ge-clathrates have indeed been obtained. Here we show that this strategy can also be applied to water-based clathrates: five days of continuous vacuum pumping on small particles of neon hydrate (of structure sII) removes all guests, allowing us to determine the crystal structure, thermal expansivity and limit of metastability of the empty hydrate. It is the seventeenth experimentally established crystalline ice phase, ice XVI according to the current ice nomenclature, has a density of 0.81 grams per cubic centimetre (making it the least dense of all known crystalline water phases) and is expected to be the stable low-temperature phase of water at negative pressures (that is, under tension). We find that the empty hydrate structure exhibits negative thermal expansion below about 55 kelvin, and that it is mechanically more stable and has at low temperatures larger lattice constants than the filled hydrate. These observations attest to the importance of kinetic effects and host-guest interactions in clathrate hydrates, with further characterization of the empty hydrate expected to improve our understanding of the structure, properties and behaviour of these unique materials.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
2.
Discounting in Economic Evaluations Attema, Arthur E.; Brouwer, Werner B. F.; Claxton, Karl
PharmacoEconomics,
07/2018, Letnik:
36, Številka:
7
Journal Article
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Appropriate discounting rules in economic evaluations have received considerable attention in the literature and in national guidelines for economic evaluations. Rightfully so, as discounting can be ...quite influential on the outcomes of economic evaluations. The most prominent controversies regarding discounting involve the basis for and height of the discount rate, whether costs and effects should be discounted at the same rate, and whether discount rates should decline or stay constant over time. Moreover, the choice for discount rules depends on the decision context one adopts as the most relevant. In this article, we review these issues and debates, and describe and discuss the current discounting recommendations of the countries publishing their national guidelines. We finish the article by proposing a research agenda.
Determining the brain perfusion is an important task for diagnosis of vascular diseases such as occlusions and intracerebral haemorrhage. Even after successful diagnosis, there is a high risk of ...restenosis or rebleeding such that patients need intense attention in the days after treatment. Within this work, we present a diagnostic tomographic imager that allows access to brain perfusion quantitatively in short intervals. The device is based on the magnetic particle imaging technology and is designed for human scale. It is highly sensitive and allows the detection of an iron concentration of 263 pmol
ml
, which is one of the lowest iron concentrations imaged by MPI so far. The imager is self-shielded and can be used in unshielded environments such as intensive care units. In combination with the low technical requirements this opens up a variety of medical applications and would allow monitoring of stroke on intensive care units.
ABSTRACT
In‐situ synchrotron X‐ray computed microtomography with sub‐micrometer voxel size was used to study the decomposition of gas hydrates in a sedimentary matrix. Xenon‐hydrate was used instead ...of methane hydrate to enhance the absorption contrast. The microstructural features of the decomposition process were elucidated indicating that the decomposition starts at the hydrate‐gas interface; it does not proceed at the contacts with quartz grains. Melt water accumulates at retreating hydrate surface. The decomposition is not homogeneous and the decomposition rates depend on the distance of the hydrate surface to the gas phase indicating a diffusion‐limitation of the gas transport through the water phase. Gas is found to be metastably enriched in the water phase with a concentration decreasing away from the hydrate‐water interface. The initial decomposition process facilitates redistribution of fluid phases in the pore space and local reformation of gas hydrates. The observations allow also rationalizing earlier conjectures from experiments with low spatial resolutions and suggest that the hydrate‐sediment assemblies remain intact until the hydrate spacers between sediment grains finally collapse; possible effects on mechanical stability and permeability are discussed. The resulting time resolved characteristics of gas hydrate decomposition and the influence of melt water on the reaction rate are of importance for a suggested gas recovery from marine sediments by depressurization.
Key Points
Time resolved, microstructural aspects of pressure‐induced gas hydrate dissolution in sediments followed with in situ synchrotron tomography
A diffusion‐limit on the liberated gas transport through the gas‐enriched water and a resulting gas concentration gradient is indicated
Possible effects of the microstructural behavior of hydrate decomposition on mechanical stability and permeability properties are discussed
...it is unsurprising that in the 2013 guidance of the National Institute for Health and Care Excellence (NICE) it was already mentioned that all direct health effects, whether for patients or, when ...relevant, carers" 18 should be included in the analysis. ...the first US Panel on Cost-Effectiveness in Health and Medicine 10, recommending the adoption of a societal perspective, encouraged researchers to think broadly about the inclusion of health effects in significant others. ...for reasons of efficiency, following the decision rules underlying economic evaluations from a healthcare or societal perspective, inclusion is warranted. 2.2Equity Systematically ignoring spillover effects cannot therefore be justified on the grounds that they do not make a difference or are irrelevant. ...evidence on spillover effects is increasing, as this special issue of PharmacoEconomics testifies, making it increasingly possible to have an idea about 'net spillover effects' whenever deemed relevant. ...it seems obvious that McCabe's suggestion of excluding spillover effects from economic evaluations and decision making is not an answer to the issue of opportunity costs and risks health lowering, inefficient and unfair decisions. 3.2 Uncertainty Including spillover effects (like any other component in an economic evaluation) may increase uncertainty, but uncertain relevant estimates are certainly better than certain irrelevant estimates of zero!
In this work we study various notions of uncertainty for angular momentum in the spin-s representation of SU(2). We characterize the 'uncertainty regions' given by all vectors, whose components are ...specified by the variances of the three angular momentum components. A basic feature of this set is a lower bound for the sum of the three variances. We give a method for obtaining optimal lower bounds for uncertainty regions for general operator triples, and evaluate these for small s. Further lower bounds are derived by generalizing the technique by which Robertson obtained his state-dependent lower bound. These are optimal for large s, since they are saturated by states taken from the Holstein-Primakoff approximation. We show that, for all s, all variances are consistent with the so-called vector model, i.e., they can also be realized by a classical probability measure on a sphere of radius Entropic uncertainty relations can be discussed similarly, but are minimized by different states than those minimizing the variances for small s. For large s the Maassen-Uffink bound becomes sharp and we explicitly describe the extremalizing states. Measurement uncertainty, as recently discussed by Busch, Lahti and Werner for position and momentum, is introduced and a generalized observable (POVM) which minimizes the worst case measurement uncertainty of all angular momentum components is explicitly determined, along with the minimal uncertainty. The output vectors for the optimal measurement all have the same length where as
We describe the alterations of classical neurotransmitters and neuropeptides in generalized epilepsy. A neuronal network in this disease is developed. Gamma aminobutyric acid (GABA) hypoactivity ...induces dopamine hyperactivity because dopaminergic neurons are affected by the inhibitory influence of the GABAergic system through GABA(A) receptors. Glutamate hyperactivity is exerted via presynaptic N-methyl-D-aspartate (NMDA) receptors, which strongly inhibit serotoninergic neurons, and via postsynaptic ionotropic glutaminergic receptors, which can induce epileptic seizures. A collection of specific subreceptors of classical neurotransmitters and neuropeptides involved in epileptogenesis is reported. The question arises whether agonists/antagonists of neuropeptides (neuropeptide Y, galanin…) could have additional antiepileptic properties. The effect of conventional and newer antiepileptic drugs interfering with these subreceptors is discussed on the basis of the neuronal network suggested. From these data, it is concluded that new antiepileptic drugs interfering with other specific subreceptors (GABA(B) antagonists, metabotropic glutaminergic receptors subtype 5 (mGlu5R) antagonists, mGlu2/3R agonists, 5-serotonin (5-HT(7)) agonists) could further stabilize the neuronal network in generalized epilepsy.
ABSTRACT
The interpretation of redshift surveys requires modelling the relationship between large-scale fluctuations in the observed number density of tracers, δh, and the underlying matter density, ...δ. Bias models often express δh as a truncated series of integro-differential operators acting on δ, each weighted by a bias parameter. Due to the presence of ‘composite operators’ (obtained by multiplying fields evaluated at the same spatial location), the linear bias parameter measured from clustering statistics does not coincide with that appearing in the bias expansion. This issue can be cured by re-writing the expansion in terms of ‘renormalized’ operators. After providing a pedagogical and comprehensive review of bias renormalization in perturbation theory, we generalize the concept to non-perturbative dynamics and successfully apply it to dark-matter haloes extracted from a large suite of N-body simulations. When comparing numerical and perturbative results, we highlight the effect of the window function employed to smooth the random fields. We then measure the bias parameters as a function of halo mass by fitting a non-perturbative bias model (both before and after applying renormalization) to the cross spectrum $P_{\delta _\mathrm{h}\delta }(k)$. Finally, we employ Bayesian model selection to determine the optimal operator set to describe $P_{\delta _\mathrm{h}\delta }(k)$ for $k\lt 0.2\, h$ Mpc−1 at redshift z = 0. We find that it includes δ, ∇2δ, δ2 and the square of the traceless tidal tensor, s2. Considering higher order terms (in δ) leads to overfitting as they cannot be precisely constrained by our data. We also notice that next-to-leading-order perturbative solutions are inaccurate for k ≳ 0.1 h Mpc−1.
Gaining health may not be the main goal of healthcare services aimed at older people, which may (also) seek to improve wellbeing. This emphasizes the need of finding appropriate outcome measures for ...economic evaluation of such services, particularly in long-term care, capturing more than only health-related quality of life (HrQol). This review assesses the usefulness of HrQol and wellbeing instruments for economic evaluations specifically aimed at older people, focusing on generic and preference-based questionnaires measuring wellbeing in particular.
We systematically searched six databases and extracted instruments used to assess HrQol and wellbeing outcomes. Instruments were compared based on their usefulness for economic evaluation of services aimed at older people (dimensions measured, availability of utility scores, extent of validation).
We identified 487 articles using 34 generic instruments: 22 wellbeing (two of which were preference-based) and 11 HrQol instruments. While standard HrQol instruments measure physical, social and psychological dimensions, wellbeing instruments contain additional dimensions such as purpose in life and achievement, security, and freedom.
We found four promising wellbeing instruments for inclusion in economic evaluation: Ferrans and Powers QLI and the WHO-Qol OLD, ICECAP-O and the ASCOT. Ferrans and Powers QLI and the WHO-Qol OLD are widely validated but lack preference-weights while for ICECAP-O and the ASCOT preference-weights are available, but are less widely validated. Until preference-weights are available for the first two instruments, the ICECAP-O and the ASCOT currently appear to be the most useful instruments for economic evaluations in services aimed at older people. Their limitations are that (1) health dimensions may be captured only partially and (2) the instruments require further validation. Therefore, we currently recommend using the ICECAP-O or the ASCOT alongside the EQ-5D or SF-6D when evaluating interventions aimed at older people.
•Economic evaluation in the curative sector is widespread and well-established using Health-related quality of life measures.•Economic evaluation in health and social care is important, but not straightforward.•Health-related quality of life measures may misrepresent the benefits of services for older people.•Wellbeing measures would be more suited for economic evaluation of older people.•Currently the most suitable measures are the ICECAP-O and the ASCOT, even though both need further validation.
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