4,621 research outputs found
CO2 laser waveguiding in proton implanted GaAs
Surface layers capable of supporting optical modes at 10.6 microns have been produced in n-type GaAs wafers through 300 keV proton implantation. The dominant mechanism for this effect appears to be free carrier compensation. Characterization of the implanted layers by analysis of infrared reflectivity spectra and synchronous coupling at 10.6 microns produced results in good agreement with elementary models. These results of sample characterization by infrared reflectivity and by CO2 laser waveguiding as implanted are presented and evaluated
RothC - A model for the turnover of carbon in soil Model description and users guide (Windows version) (updated June 2014)
Perimeter ring currents in benzenoids from Pauling bond orders
It is shown that the ring currents in perimeter hexagonal rings of Kekulean benzenoids, as estimated
within the Randić conjugated-circuit model, can be calculated directly without tedious pairwise
comparison of Kekulé structures or Kekulé counting for cycle-deleted subgraphs. Required are only
the Pauling bond orders of perimeter bonds and the number of Kekulé structures of the benzenoid,
both readily available from the adjacency matrix of the carbon skeleton. This approach provides easy
calculation of complete current maps for benzenoids in which every face has at least one bond on the
perimeter (as in the example of cata-condensed benzenoids), and allows qualitative evaluation of the
main ring-current contributions to 1H chemical shifts in general benzenoids. A combined Randić-
Pauling model for correlation of ring current and bond length through bond order is derived and shown
to be consistent with resilience of current under bond alternation
Surgical management of posterior fossa metastases
The diagnosis of brain metastases is associated with a poor prognosis reflecting uncontrolled primary disease that has spread to the relative sanctuary of the central nervous system. 20 % of brain metastases occur in the posterior fossa and are associated with significant morbidity. The risk of acute hydrocephalus and potential for sudden death means these metastases are often dealt with as emergency cases. This approach means a full pre-operative assessment and staging of underlying disease may be neglected and a proportion of patients undergo comparatively high risk surgery with little or no survival benefit. This study aimed to assess outcomes in patients to identify factors that may assist in case selection. We report a retrospective case series of 92 consecutive patients operated for posterior fossa metastases between 2007 and 2012. Routine demographic data was collected plus data on performance status, primary cancer site, details of surgery, adjuvant treatment and survival. The only independent positive prognostic factors identified on multivariate analysis were good performance status (if Karnofsky performance score >70, hazard ratio (HR) for death 0.36, 95 % confidence interval (CI) 0.18–0.69), adjuvant whole brain radiotherapy (HR 0.37, 95 % CI 0.21–0.65) and adjuvant chemotherapy where there was extracranial disease and non-synchronous presentation (HR 0.51, 95 % CI 0.31–0.82). Patients presenting with posterior fossa metastases may not be investigated as thoroughly as those with supratentorial tumours. Staging and assessment is essential however, and in the meantime emergencies related to tumour mass effect should be managed with steroids and cerebrospinal fluid diversion as required
Red Button and Yellow Button: Usable Security for Lost Security Tokens
Currently, losing a security token places the user in a dilemma: reporting the loss as soon as it is discovered involves a significant burden which is usually overkill in the common case that the token is later found behind a sofa. Not reporting the loss, on the other hand, puts the security of the protected account at risk and potentially leaves the user liable.
We propose a simple architectural solution with wide applicability that allows the user to reap the security benefit of reporting the loss early, but without paying the corresponding usability penalty if the event was later discovered to be a false alarm.The authors with a Cambridge affiliation are grateful to the European Research Council for funding this research through grant StG 307224 (Pico). Goldberg thanks NSERC for grant RGPIN-341529. We also thank the workshop attendees for comments
Fate of 15N-labelled fertilizer applied to spring barley grown on soils of contrasting nutrient status
PMH51 The Development and Validation of a Quality of Life Measure for People with Mild Cognitive Impairment (The MCQ)
Monitoring of Biodiesel Transesterification Process Using Impedance Measurement
Transesterification is commonly used to produce biodiesel from methylester. In order to control the conversion process it is often useful to employ process monitoring and in particular monitor the mass transfer processes that limit the initial reaction rates. Such monitoring of the initial phase of reaction may provide opportunity for process optimization. Previous work has identified many methods to monitor reaction progress. This paper proposes the use of a simple method which is able to provide information regarding the progress of mass transfer and chemical reaction during biodiesel production. The process uses impedance measurement. The experimentally determined impedance results clearly show the two important phases of the transesterification reaction, a mass transfer control phase followed by a kinetically controlled phase
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