Phase boundary between Na-Si clathrates of structures I and II at high pressures and high temperatures

Understanding the covalent clathrate formation is a crucial point for the design of new superhard materials with intrinsic coupling of superhardness and metallic conductivity. Silicon clathrates have the archetype structures that can serve an existant model compounds for superhard clathrate frameworks "Si-B", "Si-C", "B-C" and "C" with intercalated atoms (e.g. alkali metals or even halogenes) that can assure the metalic properties. Here we report the in situ and ex situ studies of high-pressure formation and stability of clathrates Na8Si46 (structure I) and Na24+xSi136 (structure II). Experiments have been performed using standard Paris-Edinburgh cells (opposite anvils) up to 6 GPa and 1500 K. We have established that chemical interactions in Na-Si system and transition between two structures of clathrates occur at temperatures below silicon melting. The strong sensitivity of crystallization products to the sodium concentration have been observed. A tentative diagram of clathrate transformations has been proposed. At least up to ~6 GPa, Na24+xSi136 (structure II) is stable at lower temperatures as compared to Na8Si46 (structure I)

Methods and contexts: Challenges of planning with scenarios in a hospital's division

Scenario planning is presented as a well-suited approach in uncertain environments such as healthcare systems. In this article, we report a project aimed at defining scenarios in the cancer division of a large hospital. The approach chosen was based on La Prospective school of scenario planning. The project stopped before scenarios could be elaborated, for lack of knowledge available on contextual factors influencing the system. From the analysis of this case study, we elaborate on the adequacy of scenario planning in the context of small healthcare delivery organisations. We conclude that most forms of scenario planning are unlikely to work in these cases, especially in the La Prospective approach. Perspectives are drawn for scenario planning in hospitals, and for research on the fit between scenario approaches and application contexts, in order to understand what approaches work in which circumstances

Holistic assessment of call centre performance

In modern call centres 60–70% of the operational costs come in the form of the human agents who take the calls. Ensuring that the call centre operates at lowest cost and maximum efficiency involves a trade‐off of the cost of agents against lost revenue and increased customer dissatisfaction due to lost calls. Modelling the performance characteristics of a call centre in terms of the agent queue alone misses key performance influencers, specifically the interaction between channel availability at the media gateway and the time a call is queued. A blocking probability at the media gateway, as low as 0.45%, has a significant impact on the degree of queuing observed and therefore the cost and performance of the call centre. Our analysis also shows how abandonment impacts queuing delay. However, the call centre manager has less control over this than the level of contention at the media gateway. Our commercial assessment provides an evaluation of the balance between abandonment and contention, and shows that the difference in cost between the best and worst strategy is £130K per annum, however this must be balanced against a possible additional £2.98 m exposure in lost calls if abandonment alone is used

Call centers with a postponed callback offer

We study a call center model with a postponed callback option. A customer at the head of the queue whose elapsed waiting time achieves a given threshold receives a voice message mentioning the option to be called back later. This callback option differs from the traditional ones found in the literature where the callback offer is given at customer’s arrival. We approximate this system by a two-dimensional Markov chain, with one dimension being a unit of a discretization of the waiting time. We next show that this approximation model converges to the exact one. This allows us to obtain explicitly the performance measures without abandonment and to compute them numerically otherwise. From the performance analysis, we derive a series of practical insights and recommendations for a clever use of the callback offer. In particular, we show that this time-based offer outperforms traditional ones when considering the waiting time of inbound calls

Benthic foraminifera as tracers of brine production in the Storfjorden "sea ice factory"

The rapid response of benthic foraminifera to environmental factors (e.g. organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such an approach, however, requires a thorough knowledge of their modern ecology in such extreme settings. To this aim, seven stations along a north-south transect across the Storfjorden (Svalbard archipelago) have been sampled using an interface multicorer. This fjord is an area of intense sea ice formation characterised by the production of brine-enriched shelf waters (BSW) as a result of a recurrent latent-heat polynya. Living (rose bengal-stained) foraminiferal assemblages were analysed together with geochemical and sedimentological parameters in the top 5 cm of the sediment. Three major biozones were distinguished. (i) The inner fjord zone, dominated by typical glacier proximal calcareous species, which opportunistically respond to fresh organic matter inputs. (ii) The deep basins and sill zone, characterised by glacier distal agglutinated fauna; these are either dominant because of the mostly refractory nature of organic matter and/or the brine persistence that hampers the growth of calcareous species and/or causes their dissolution. (iii) The outer fjord zone, characterised by typical North Atlantic species due to the intrusion of the North Atlantic water in the Storfjordrenna. The stressful conditions present in the deep basins and sill (i.e. acidic waters and low food quality) result in a high agglutinated = calcareous ratio (A=C). This supports the potential use of the A=C ratio as a proxy for brine persistence and overflow in Storfjorden

Spherical Polyelectrolyte Brushes Templated Hollow C MnO Nanospheres as Sulfur Host Materials for Li S Batteries

Li amp; 8722;S battery has been considered as the next generation energy storage device, which still suffers from the shuttle effect of lithium polysulfides LiPSs . In this work, mesoporous hollow carbon coated MnO nanospheres C MnO have been designed and synthesized using spherical polyelectrolyte brushes SPB as template, KMnO4 as MnO precursor, and polydopamine as carbon source to improve the electrochemical performance of Li amp; 8722;S battery. The hollow C MnO nanospheres enable the combination of physical confinement and chemical adsorption of the LiPSs. The thin carbon coating layer can provide good electrical conductivity and additional physical confinement to polysulfides. Moreover, the encapsulated MnO inside the carbon shell exhibits strong chemical adsorption to polysulfides. The constructed C MnO S cathode shows the discharge capacity of 1026 amp; 8197;mAh amp; 8201;g amp; 8722;1 at 0.1 amp; 8197;C with 79 capacity retention after 80 cycles. The synthesized hollow C MnO nanoparticles can work as highly efficient sulfur host materials, providing an effective solution to suppress the shuttle effect in Li amp; 8722;S batter

Characterization of CTX-M ESBLs in Enterobacter cloacae, Escherichia coli and Klebsiella pneumoniae clinical isolates from Cairo, Egypt

<p>Abstract</p> <p>Background</p> <p>A high rate of resistance to 3^rdgeneration cephalosporins among Enterobacteriaceae isolates from Egypt has been previously reported. This study aims to characterize the resistance mechanism (s) to extended spectrum cephalosporins among resistant clinical isolates at a medical institute in Cairo, Egypt.</p> <p>Methods</p> <p>Nonconsecutive <it>Klebsiella pneumoniae </it>(Kp), <it>Enterobacter cloacae </it>(ENT) and <it>Escherichia coli </it>(EC) isolates were obtained from the clinical laboratory at the medical institute. Antibiotic susceptibility was tested by CLSI disk diffusion and ESBL confirmatory tests. MICs were determined using broth microdilution. Isoelectric focusing (IEF) was used to determine the pI values, inhibitor profiles, and cefotaxime (CTX) hydrolysis by the β-lactamases. PCR and sequencing were performed using <it>bla</it>_CTX-Mand IS<it>Ecp1</it>-specific primers, with DNA obtained from the clinical isolates. Conjugation experiments were done to determine the mobility of <it>bla</it>_CTX-M.</p> <p>Results</p> <p>All five clinical isolates were resistant to CTX, and were positive for ESBL screening. IEF revealed multiple β-lactamases produced by each isolate, including a β-lactamase with a pI of 8.0 in Kp and ENT and a β-lactamase with a pI of 9.0 in EC. Both β-lactamases were inhibited by clavulanic acid and hydrolyzed CTX. PCR and sequence analysis identified <it>bla</it>_CTX-M-14in Kp and ENT and a <it>bla</it>_CTX-M-15in EC. Both <it>bla</it>_CTX-M-14and <it>bla</it>_CTX-M-15were preceded by IS<it>Ecp1 </it>elements as revealed by partial sequence analysis of the upstream region of the <it>bla</it>_CTX-Mgenes. <it>bla</it>_CTX-M-15 was transferable but not <it>bla</it>_CTX-M-14.</p> <p>Conclusion</p> <p>This is the first report of CTX-M-14 in Kp and ENT isolates from Egypt, the Middle East and North Africa.</p

Optimal Reinsurance with One Insurer and Multiple Reinsurers

In this paper, we consider a one-period optimal reinsurance design model with n reinsurers and an insurer. For very general preferences of the insurer, we obtain that there exists a very intuitive pricing formula for all reinsurers that use a distortion premium principle. The insurer determines its optimal risk that it wants to reinsure via this pricing formula. This risk it wants to reinsure is then shared by the reinsurers via tranching. The optimal ceded loss functions among multiple reinsurers are derived explicitly under the additional assumptions that the insurer’s preferences are given by an inverse-S shaped distortion risk measure and that the reinsurer’s premium principles are some functions of the Conditional Value-at-Risk. We also demonstrate that under some prescribed conditions, it is never optimal for the insurer to cede its risk to more than two reinsurers