Trapping of diffusive particles by rough absorbing surfaces: boundary smoothing approach

We present analytical results for the first-passage statistics of Brownian particles near a comblike absorbing boundary. Our approach is based on the method of boundary homogenization (or boundary smoothing) when an equivalent flat boundary is introduced to maintain the same diffusion flux as the original rough boundary. By using the conformal invariance of the Laplace equation we derive an analytic expression for the position of an equivalent boundary in terms of its spatial period and amplitude. The main analytical results being initially obtained for the steady state system provide important insights into the statistical characteristics of diffusive transport near rough boundaries (high order moments of the trapping time statistics).

A Stiffness Reduction Method for efficient absorption of waves at boundaries for use in commercial Finite Element codes

Commercially available Finite Element packages are being used increasingly for modelling elastic wave propagation problems. Demand for improved capability has resulted in a drive to maximise the efficiency of the solver whilst maintaining a reliable solution. Modelling waves in unbound elastic media to high levels of accuracy presents a challenge for commercial packages, requiring the removal of unwanted reflections from model boundaries. For time domain explicit solvers, Absorbing Layers by Increasing Damping (ALID) have proven successful because they offer flexible application to modellers and, unlike the Perfectly Matched Layers (PMLs) approach, they are readily implemented in most commercial Finite Element software without requiring access to the source code. However, despite good overall performance, this technique requires the spatial model to extend significantly outside the domain of interest. Here, a Stiffness Reduction Method (SRM) has been developed that operates within a significantly reduced spatial domain. The technique is applied by altering the damping and stiffness matrices of the system, inducing decay of any incident wave. Absorbing region variables are expressed as a function of known model constants, helping to apply the technique to generic elastodynamic problems. The SRM has been shown to perform significantly better than ALID, with results confirmed by both numerical and analytical means.

Colonic decompression and direct intraluminal medical therapy for Clostridium difficile-associated megacolon using a tube placed endoscopically in the proximal colon

AIM

Urgent colectomy for severe Clostridium difficile infection can be associated with increased morbidity and mortality. We aimed to use endoscopic methods for treatment.

METHOD

We describe a technique of placing an intracolonic tube facilitating decompression and direct delivery of vancomycin to the proximal colon along with enemas on a regular and frequent basis that may not be possible with vancomycin enemas alone.

RESULTS

Successful resolution of the C. difficile infection and avoidance of surgery.

CONCLUSION

While further long-term evaluation is required, our initial results have shown it to be effective in treating select patients with recalcitrant Clostridium difficile-associated megacolon.

Prospective study of injury severity scores during a season of British Superbike racing

Background:

Motorbike racing is considered by many to be a dangerous sport, but there are little data within the literature to support this view. The purpose of this study was to determine the injury severity scores of injured riders in order to assess injury severity in elite level motorbike racing.

Methods:

Injury data were prospectively collected from all riders who attended the circuit medical centres at all rounds of the 2011 British Superbike Season. Abbreviated injury score and injury severity score were calculated for each rider and recorded along with other rider demographics.

Results:

A total of 259 riders presented to the circuit medical centres with injuries during the 2011 season. They suffered 382 injuries between them, with one fatality. The median injury severity score was 1 (mean 3.28, range 1–48, SD 5.08). Of the 1010 fallers during the season, only 33 (3.3%) required acute hospital admission.

Conclusion:

Greater than 93% of injured riders had injuries with an injury severity score ≤ 8 which is likely related to the high degree of protective clothing worn and safety measures at circuits including air fencing. The injury severity scores presented here for motorbike racing are less than or comparable to those seen in other physical sports such as elite level horse riding.

When it is not a Spigelian Hernia: Abdominal Cutaneous Nerve Entrapment Syndrome

Abdominal wall pain at the linea semilunaris is classically the result of a Spigelian hernia. If no hernia is detected, these patients may be left with chronic pain without a diagnosis or treatment. A retrospective review was performed of patients presenting with abdominal wall pain at the linea semilunaris between 2009 and 2012. Of the 14 patients, three (21%) were diagnosed with a Spigelian hernia confirmed by imaging. The remaining patients were eventually diagnosed with abdominal cutaneous nerve entrapment syndrome (ACNES). The average delay in diagnosis was 4 years with patients with ACNES suffering twice as long with chronic pain. Patients with a Spigelian hernia and ACNES had different demographics and presenting complaints. Physical examination findings were nondiagnostic. Of the patients with ACNES, five (50%) had resolution of pain with serial nerve blocks alone; another five proceeded to surgical neurectomy with resolution of their pain. Thus, to prevent delay in diagnosis and treatment, patients with chronic abdominal wall pain at the linea semilunaris should first be ruled out for Spigelian hernia. Then, they should be evaluated and treated for ACNES.

When it is not a Spigelian hernia: abdominal cutaneous nerve entrapment syndrome

Abdominal wall pain at the linea semilunaris is classically the result of a Spigelian hernia. If no hernia is detected, these patients may be left with chronic pain without a diagnosis or treatment. A retrospective review was performed of patients presenting with abdominal wall pain at the linea semilunaris between 2009 and 2012. Of the 14 patients, three (21%) were diagnosed with a Spigelian hernia confirmed by imaging. The remaining patients were eventually diagnosed with abdominal cutaneous nerve entrapment syndrome (ACNES). The average delay in diagnosis was 4 years with patients with ACNES suffering twice as long with chronic pain. Patients with a Spigelian hernia and ACNES had different demographics and presenting complaints. Physical examination findings were nondiagnostic. Of the patients with ACNES, five (50%) had resolution of pain with serial nerve blocks alone; another five proceeded to surgical neurectomy with resolution of their pain. Thus, to prevent delay in diagnosis and treatment, patients with chronic abdominal wall pain at the linea semilunaris should first be ruled out for Spigelian hernia. Then, they should be evaluated and treated for ACNES.

Opportunities and strategies to further reduce animal use for Leptospira vaccine potency testing

Hamsters are routinely infected with virulent Leptospira for two purposes in the regulation of biologics: the performance of Codified potency tests and maintenance of challenge culture for the Codified potency tests. Options for reducing animal use in these processes were explored in a plenary lecture at the "International Workshop on Alternative Methods for Leptospira Vaccine Potency Testing: State of the Science and the Way Forward" held at the Center for Veterinary Biologics in September 2012. The use of validated in vitro potency assays such as those developed by the U.S. Department of Agriculture for Leptospira (L.) canicola, Leptospira grippotyphosa, Leptospira pomona, and Leptospira icterohaemorrhagiae rather than the Codified hamster vaccination-challenge assay was encouraged. Alternatives such as reduced animal numbers in the hamster vaccination-challenge testing were considered for problematic situations. Specifically, the merits of sharing challenge controls, reducing group sizes, and eliminating animals for concurrent challenge dose titration were assessed. Options for maintaining virulent, stable cultures without serial passage through hamsters or with decreased hamster use were also discussed. The maintenance of virulent Leptospira without the use of live animals is especially difficult since a reliable means to maintain virulence after multiple in vitro passages has not yet been identified.

USDA regulatory guidelines and practices for veterinary Leptospira vaccine potency testing

Batch-release potency testing of leptospiral vaccines licensed by the United States Department of Agriculture (USDA) historically was conducted through animal vaccination-challenge models. The hamster vaccination-challenge assay was Codified in 1974 for bacterins containing Leptospira pomona, Leptospira icterohaemorrhagiae, and Leptospira canicola, and in 1975 for bacterins containing Leptospira grippotyphosa. In brief, 10 hamsters are vaccinated with a specified dilution of bacterin. After a holding period, the vaccinated hamsters, as well as nonvaccinated controls, are challenged with virulent Leptospira and observed for mortality. Eighty percent of vaccinated hamsters must survive in the face of a valid challenge. The high cost of the Codified tests, in terms of monetary expense and animal welfare, prompted the Center for Veterinary Biologics (CVB) to develop ELISA alternatives for them. Potency tests for other serogroups, such as Leptospira hardjo-bovis, that do not have Codified requirements for potency testing continue to be examined on a case-by-case basis.