Worcester Polytechnic Institute

About: Worcester Polytechnic Institute is a education organization based out in Worcester, Massachusetts, United States. It is known for research contribution in the topics: Population & Data envelopment analysis. The organization has 6270 authors who have published 12704 publications receiving 332081 citations. The organization is also known as: WPI.

Scaling of Fully Pulsed Jets in Crossflow

Abstract: There is recent interest in the dynamics of pulsed jets in uniform crossflow. A classification scheme for fully pulsed Jets in crossflow is proposed based on the stroke ratio of the jet pulse and the duty cycle of the pulse train. Scaling relations for penetration and dilution of fully pulsed jets'in crossflow are derived from the self-similar scaling of turbulent vortex rings and puffs in quiescent media. Individual turbulent structures are assumed to drift freely with the crossflow in the proposed scaling. The penetration of fully pulsed jets scales with the fourth root of the velocity ratio, stroke ratio, and axial distance. The decay of mean concentration scales with the velocity ratio and axial distance to the -3/4th power. These scaling relations apply to distinct turbulent structures before any interaction between successive structures. The criteria for interaction among flow structures near the nozzle and in the far field are also presented.

Radioactive microsphere validation of a volume localized continuous saturation perfusion measurement.

Abstract: Detre et al. (Magn. Reson. Med. 23, 37-45 (1992)) and Zhang et al., (Magn. Reson. Med. 25, 362 (1992)) have recently demonstrated a technique for the measurement of regional cerebral blood flow (rCBF) based on the continuous saturation (or inversion) of the arterial blood supply to the brain in rats at 4.7 T. In the work reported here, we combined this technique with volume localized (PRESS) readouts to benefit from recording "perfusion" signals averaged over a larger volume, resulting in rapid acquisition of data with sufficient signal-to-noise ratio for application at 2.0 T. In 10 baseline flow measurements, the mean error between the NMR technique and the microsphere flow measurement was -1.5% with a standard deviation of 15.2%. For five measurements obtained with occlusion of the middle cerebral artery, the mean error was -32.4 +/- 20.2%. Perfusion measurements from a single animal under hypercapnic conditions indicated that the NMR technique could underestimate rCBF at high flow rates. An error analysis of the NMR perfusion model is also presented, along with results for typical parameters encountered at 2.0 T.

Prognostic factors in adult brainstem gliomas: a multicenter, retrospective analysis of 101 cases

Abstract: Background Adult brainstem gliomas (BSG) are uncommon and poorly understood with respect to prognostic factors. We retrospectively evaluated the clinical, radiographic, histologic, and treatment features from 101 adults with presumed or biopsy proven BSG to determine prognostic factors. Patients and Methods We reviewed the records of patients diagnosed from 1987–2005. We used Cox proportional hazard models to determine prognostic factors. Results These 50 male and 51 female patients ranged in age from 18 to 79 years at diagnosis (median 36 years) with follow-ups from 1 to 261 months (median 47 months). The overall survival for all patients at 5 and 10 years was 58% and 41%, respectively, with a median survival of 85 months (range 1–228). Out of 24 candidate prognosis factors, we selected seven covariates for proportional hazards model by Lasso procedure: age of diagnosis, ethnicity, need for corticosteroids, tumor grade, dysphagia, tumor location, and karnofsky performance status (KPS). Univariate analysis showed that these seven factors are significantly associated with survival. Multivariate analysis showed that four covariates significantly increased hazard for survival: ethnicity, tumor location, age of diagnosis, and tumor grade. Conclusions In this study, we identified four prognostic factors that were significantly associated with survival in adults with BSGs. Overall, these patients have a better prognosis than children with BSGs reported in the literature. These results call for larger prospective studies to fully assess the importance of these factors in the clinical setting and to help stratify patients in future clinical studies.

Computer‐aided fixture design verification

Abstract: Computer‐aided fixture design (CAFD) techniques have been advanced so rapidly that computers can now generate fixture configurations automatically, for both modular fixtures and dedicated fixtures. Computer‐aided fixture design verification (CAFDV) is the techniques for verifying and improving existing fixture designs. It verifies the followings: geometric constraining ability, achieved tolerance, fixturing stability, and fixturing accessibility. Two models – one geometric and one kinematic – are created for the verification.

Cross Processor Cache Attacks

Abstract: Multi-processor systems are becoming the de-facto standard across different computing domains, ranging from high-end multi-tenant cloud servers to low-power mobile platforms. The denser integration of CPUs creates an opportunity for great economic savings achieved by packing processes of multiple tenants or by bundling all kinds of tasks at various privilege levels to share the same platform. This level of sharing carries with it a serious risk of leaking sensitive information through the shared microarchitectural components. Microarchitectural attacks initially only exploited core-private resources, but were quickly generalized to resources shared within the CPU. We present the first fine grain side channel attack that works across processors. The attack does not require CPU co-location of the attacker and the victim. The novelty of the proposed work is that, for the first time the directory protocol of high efficiency CPU interconnects is targeted. The directory protocol is common to all modern multi-CPU systems. Examples include AMD's HyperTransport, Intel's Quickpath, and ARM's AMBA Coherent Interconnect. The proposed attack does not rely on any specific characteristic of the cache hierarchy, e.g. inclusiveness. Note that inclusiveness was assumed in all earlier works. Furthermore, the viability of the proposed covert channel is demonstrated with two new attacks: by recovering a full AES key in OpenSSL, and a full ElGamal key in libgcrypt within the range of seconds on a shared AMD Opteron server.