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We provide a framework for reasoning about information-hiding requirements in multiagent systems and for reasoning about anonymity in particular. Our framework employs the modal logic of knowledge within the context of the runs and systems framework, much in the spirit of our earlier work on secrecy [Halpern and O'Neill 2002]. We give several definitions of anonymity with respect to agents, actions, and observers in multiagent systems, and we relate our definitions of anonymity to other definitions of information hiding, such as secrecy. We also give probabilistic definitions of anonymity that are able to quantify an observer's uncertainty about the state of the system. Finally, we relate our definitions of anonymity to other formalizations of anonymity and information hiding, including definitions of anonymity in the process algebra CSP and definitions of information hiding using function views.

Interactive programs allow users to engage in input and output throughout execution. The ubiquity of such programs motivates the development of models for reasoning about their information-flow security, yet no such models seem to exist for imperative programming languages. Further, existing language-based security conditions founded on noninteractive models permit insecure information flows in interactive imperative programs. This paper formulates new strategybased information-flow security conditions for a simple imperative programming language that includes input and output operators. The semantics of the language enables a fine-grained approach to the resolution of nondeterministic choices. The security conditions leverage this approach to prohibit refinement attacks while still permitting observable nondeterminism. Extending the language with probabilistic choice yields a corresponding definition of probabilistic noninterference. A soundness theorem demonstrates the feasibility of statically enforcing the security conditions via a simple type system. These results constitute a step toward understanding and enforcing information-flow security in real-world programming languages, which include similar input and output operators.

Object Surgical site infection (SSI) is a morbid complication with high cost in spine surgery. In this era of health care reforms, adjuvant therapies that not only improve quality but also decrease cost are considered of highest value. The authors introduced local application of vancomycin powder into their practice of posterior spinal fusion for spine trauma and undertook this study to determine the value and cost benefit of using vancomycin powder in surgical sites to prevent postoperative infections. Methods A retrospective review of 110 patients with traumatic spine injuries treated with instrumented posterior spine fusions over a 2-year period at a single institution was performed. One group (control group) received standard systemic prophylaxis only, whereas another (treatment group) received 1 g of locally applied vancomycin powder (spread over the surgical wound) in addition to systemic prophylaxis. Data were collected on patient demographic characteristics, clinical variables, surgical variables, and 90-day morbidity. Incidence of infection was the primary outcome evaluated, and billing records were reviewed to determine total infection-related medical cost (cost of reoperation/wound debridement, medications, and diagnostic tests). The payer's cost was estimated to be 70% of the total billing cost. Results A total of 110 patients were included in the study. The control (n = 54) and treatment groups (n = 56) were similar at baseline. Use of vancomycin powder led to significant reduction in infection rate (13% infection rate in the control group vs 0% in the treatment group, p = 0.02). There were no adverse effects noted from the use of vancomycin powder. The total mean cost of treating postoperative infection per patient was $33,705. Use of vancomycin powder led to a cost savings of $438,165 per 100 posterior spinal fusions performed for traumatic injuries. Conclusions The use of adjuvant vancomycin powder was associated with a significant reduction in the incidence of postoperative infection as well as infection-related medical cost. These findings suggest that use of adjuvant vancomycin powder in high-risk patients undergoing spinal fusion is a cost-saving option for preventing postoperative infections, as it can lead to cost-savings of $438,165 per 100 spinal fusions performed.

The McCulloch retractor generates a higher IMP than the Norfolk and Norwich retractor. However, postoperative improvement in VAS, ODI, and SF-36 scores in these patients was associated with a shorter duration of muscle retraction and not the degree of IMP or IPP generated. In this respect, periodic relaxation of the paraspinal muscle retractors during surgery to allow muscle perfusion may help to reduce postoperative back pain and disability.