21,860 research outputs found
An experimental study of the sources of fluctuating pressure loads beneath swept shock/boundary-layer interactions
An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three dimensional shock wave/boundary layer interactions is described. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins at angle of attack. Fin angles from 10 to 20 deg at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers flush-mounted in the flat plate are used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their ring levels, amplitude distributions, and power spectra, are also determined. Measurements were made for the first time in the aft regions of these interactions, revealing fluctuating pressure levels as high as 160 dB. These fluctuations are dominated by low frequency (0-5 kHz) signals. The maximum ring levels in the interactions show an increasing trend with increasing interaction strength. On the other hand, the maximum ring levels in the forward portion of the interactions decrease linearly with increasing interaction sweep back. These ring pressure distributions and spectra are correlated with the features of the interaction flowfield. The unsteadiness of the off-surface flowfield is studied using a new, non-intrusive technique based on the shadow graph method. The results indicate that the entire lambda-shock structure generated by the interaction undergoes relatively low-frequency oscillations. Some regions where particularly strong fluctuations are generated were identified. Fluctuating pressure measurements are also made along the line of symmetry of an axisymmetric jet impinging upon a flat plate at an angle. This flow was chosen as a simple analog to the impinging jet region found in the rear portion of the shock wave/boundary layer interactions under study. It is found that a sharp peak in ring pressure level exists at or near the mean stagnation point. It is suggested that the phenomena responsible for this peak may be active in the swept interactions as well, and may cause the extremely high fluctuating pressures observed in the impinging jet region in the present experimental program
Blood pressure response to Cold Pressor Test in the children of hypertensives
Two hundred student volunteers of 16-24 yrs were divided into two groups of 100 each, as children of hypertensive and children of normotensive parents. It was observed that there was no difference in resting SBP and DBP in both groups before CPT. After CPT, significant higher values of SBP after immersion, DBP after immersion, difference of SBP and difference of DBP were observed in children of hypertensive parents as compared to children of normotensive parents. This study can be used as a predictor of future development of hypertension for which early preventive measures can be taken to reduce the morbidity and mortality due to hypertensive complications
Optimal Active Social Network De-anonymization Using Information Thresholds
In this paper, de-anonymizing internet users by actively querying their group
memberships in social networks is considered. In this problem, an anonymous
victim visits the attacker's website, and the attacker uses the victim's
browser history to query her social media activity for the purpose of
de-anonymization using the minimum number of queries. A stochastic model of the
problem is considered where the attacker has partial prior knowledge of the
group membership graph and receives noisy responses to its real-time queries.
The victim's identity is assumed to be chosen randomly based on a given
distribution which models the users' risk of visiting the malicious website. A
de-anonymization algorithm is proposed which operates based on information
thresholds and its performance both in the finite and asymptotically large
social network regimes is analyzed. Furthermore, a converse result is provided
which proves the optimality of the proposed attack strategy
Seeded Graph Matching: Efficient Algorithms and Theoretical Guarantees
In this paper, a new information theoretic framework for graph matching is
introduced. Using this framework, the graph isomorphism and seeded graph
matching problems are studied. The maximum degree algorithm for graph
isomorphism is analyzed and sufficient conditions for successful matching are
rederived using type analysis. Furthermore, a new seeded matching algorithm
with polynomial time complexity is introduced. The algorithm uses `typicality
matching' and techniques from point-to-point communications for reliable
matching. Assuming an Erdos-Renyi model on the correlated graph pair, it is
shown that successful matching is guaranteed when the number of seeds grows
logarithmically with the number of vertices in the graphs. The logarithmic
coefficient is shown to be inversely proportional to the mutual information
between the edge variables in the two graphs
Quantitative weighted estimates for Rubio de Francia's Littlewood--Paley square function
We consider the Rubio de Francia's Littlewood--Paley square function
associated with an arbitrary family of intervals in with finite
overlapping. Quantitative weighted estimates are obtained for this operator.
The linear dependence on the characteristic of the weight turns
out to be sharp for , whereas the sharpness in the range
remains as an open question. Weighted weak-type estimates in the endpoint
are also provided. The results arise as a consequence of a sparse domination
shown for these operators, obtained by suitably adapting the ideas coming from
Benea (2015) and Culiuc et al. (2016).Comment: 18 pages. Revised versio
Optimal cooperative control synthesis of active displays
A technique is developed that is intended to provide a systematic approach to synthesizing display augmentation for optimal manual control in complex, closed-loop tasks. A cooperative control synthesis technique, previously developed to design pilot-optimal control augmentation for the plant, is extended to incorporate the simultaneous design of performance enhancing displays. The technique utilizes an optimal control model of the man in the loop. It is applied to the design of a quickening control law for a display and a simple K/s(2) plant, and then to an F-15 type aircraft in a multi-channel task. Utilizing the closed loop modeling and analysis procedures, the results from the display design algorithm are evaluated and an analytical validation is performed. Experimental validation is recommended for future efforts
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