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Search Results: 1 - 10 of 192256 matches for " Carl G Tams "
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Expiratory time constant for determinations of plateau pressure, respiratory system compliance, and total resistance
Nawar Al-Rawas, Michael J Banner, Neil R Euliano, Carl G Tams, Jeff Brown, A Daniel Martin, Andrea Gabrielli
Critical Care , 2013, DOI: 10.1186/cc12500
Abstract: Adults (n = 92) with acute respiratory failure were categorized into four groups depending on the mode of ventilatory support ordered by attending physicians, i. e., volume controlled - continuous mandatory ventilation (VC-CMV), volume controlled - synchronized intermittent mandatory ventilation (VC-SIMV), volume control plus (VC+), and pressure support ventilation (PSV). Positive end expiratory pressure as ordered was combined with all aforementioned modes. Pplt, determined by the traditional end inspiratory pause (EIP) method, was combined in equations to determine Crs and Rtot. Following that, the tauE method was employed, tauE was estimated from point-by-point measurements of exhaled tidal volume and flow rate, it was then combined in equations to determine Pplt, Crs, and Rtot. Both methods were compared using regression analysis.tauE, ranging from mean values of 0.54 sec to 0.66 sec, was not significantly different among ventilatory modes. The tauE method was an excellent predictor of Pplt, Crs, and Rtot for various ventilatory modes; r2 values for the relationships of E and EIP methods ranged from 0.94 to 0.99 for Pplt, 0.90 to 0.99 for Crs, and 0.88 to 0.94 for Rtot (p < 0.001). Bias and precision values were negligible.We found the tauE method was just as good as the EIP method for determining Pplt, Crs, and Rtot for various modes of ventilatory support for patients with acute respiratory failure. It is unclear if the tauE method can be generalized to patients with chronic obstructive lung disease. tauE is determined during passive deflation of the lungs without the need for changing the ventilatory mode and disrupting a patient's breathing. The tauE method obviates the need to apply an EIP, allows for continuous and automatic surveillance of inspiratory Pplt so it can be maintained [less than or equal to] 30 cm H2O for lung protection and patient safety, and permits real time assessments of pulmonary mechanics.
Attacks and Countermeasures in Fingerprint Based Biometric Cryptosystems
Benjamin Tams
Computer Science , 2013,
Abstract: We investigate implementations of biometric cryptosystems protecting fingerprint templates (which are mostly based on the fuzzy vault scheme by Juels and Sudan in 2002) with respect to the security they provide. We show that attacks taking advantage of the system's false acceptance rate, i.e. false-accept attacks, pose a very serious risk --- even if brute-force attacks are impractical to perform. Our observations lead to the clear conclusion that currently a single fingerprint is not sufficient to provide a secure biometric cryptosystem. But there remain other problems that can not be resolved by merely switching to multi-finger: Kholmatov and Yanikoglu in 2007 demonstrated that it is possible to break two matching vault records at quite a high rate via the correlation attack. We propose an implementation of a minutiae fuzzy vault that is inherently resistant against cross-matching and the correlation attack. Surprisingly, achieving cross-matching resistance is not at the cost of authentication performance. In particular, we propose to use a randomized decoding procedure and find that it is possible to achieve a GAR=91% at which no false accepts are observed on a database generally used. Our ideas can be adopted into an implementation of a multibiometric cryptosystem. All experiments described in this paper can fully be reproduced using software available for download.
Decodability Attack against the Fuzzy Commitment Scheme with Public Feature Transforms
Benjamin Tams
Computer Science , 2014,
Abstract: The fuzzy commitment scheme is a cryptographic primitive that can be used to store biometric templates being encoded as fixed-length feature vectors protected. If multiple related records generated from the same biometric instance can be intercepted, their correspondence can be determined using the decodability attack. In 2011, Kelkboom et al. proposed to pass the feature vectors through a record-specific but public permutation process in order to prevent this attack. In this paper, it is shown that this countermeasure enables another attack also analyzed by Simoens et al. in 2009 which can even ease an adversary to fully break two related records. The attack may only be feasible if the protected feature vectors have a reasonably small Hamming distance; yet, implementations and security analyses must account for this risk. This paper furthermore discusses that by means of a public transformation, the attack cannot be prevented in a binary fuzzy commitment scheme based on linear codes. Fortunately, such transformations can be generated for the non-binary case. In order to still be able to protect binary feature vectors, one may consider to use the improved fuzzy vault scheme by Dodis et al. which may be secured against linkability attacks using observations made by Merkle and Tams.
Security of the Improved Fuzzy Vault Scheme in the Presence of Record Multiplicity (Full Version)
Johannes Merkle,Benjamin Tams
Computer Science , 2013,
Abstract: Dodis et al. proposed an improved version of the fuzzy vault scheme, one of the most popular primitives used in biometric cryptosystems, requiring less storage and leaking less information. Recently, Blanton and Aliasgari have shown that the relation of two improved fuzzy vault records of the same individual may be determined by solving a system of non-linear equations. However, they conjectured that this is feasible for small parameters only. In this paper, we present a new attack against the improved fuzzy vault scheme based on the extended Euclidean algorithm that determines if two records are related and recovers the elements by which the protected features, e.g., the biometric templates, differ. Our theoretical and empirical analysis demonstrates that the attack is very effective and efficient for practical parameters. Furthermore, we show how this attack can be extended to fully recover both feature sets from related vault records much more efficiently than possible by attacking each record individually. We complement this work by deriving lower bounds for record multiplicity attacks and use these to show that our attack is asymptotically optimal in an information theoretic sense. Finally, we propose remedies to harden the scheme against record multiplicity attacks.
Dentable functions and radially uniform quasi-convexity
Carl G. Looney
International Journal of Mathematics and Mathematical Sciences , 1978, DOI: 10.1155/s0161171278000538
Abstract: In this paper we give a further result which states sufficient conditions for the theory of convergence of minimizing sequences to be applicable, develop the theory further, and give an application.
Generalizing Jeffrey Conditionalization
Carl G. Wagner
Computer Science , 2013,
Abstract: Jeffrey's rule has been generalized by Wagner to the case in which new evidence bounds the possible revisions of a prior probability below by a Dempsterian lower probability. Classical probability kinematics arises within this generalization as the special case in which the evidentiary focal elements of the bounding lower probability are pairwise disjoint. We discuss a twofold extension of this generalization, first allowing the lower bound to be any two-monotone capacity and then allowing the prior to be a lower envelope.
Resolution of cell-mediated airways diseases
Carl G Persson, Lena Uller
Respiratory Research , 2010, DOI: 10.1186/1465-9921-11-75
Abstract: Mechanisms active in development of cell-mediated airways disease such as asthma and chronic obstructive pulmonary disease (COPD) may differ from mechanisms involved in exacerbations of these diseases. Different mechanisms again would be involved in resolution of inflammation and healing of the diseased airways. A major aspect of resolution is the elimination of inflammatory cells from the diseased airway wall. This is accomplished, it is thought, by activation of a programmed cell death (apoptosis) followed by 'silent' elimination through phagocytosis of the apoptotic cells. Based on their potential to induce apoptosis of eosinophils and lymphocytes, and increase phagocytosis of apoptotic leukocytes, the mainstay airway anti-inflammatory drugs, glucocorticoids, are considered as pro-resolution drugs ([1], and references cited therein). However, it appears that few in vivo data have been publicised during the last two decades in support of a significant role of leukocyte apoptosis in airways diseases, whether steroid treatment has been involved or not. This limited support for a central dogma on resolution may increasingly be realised by authors involved in research on respiratory disorders: Downey et al [2] recently observed that findings of reduced neutrophil apoptosis in resolving exacerbations of cystic fibrosis "seem counter intuitive as it should be expected that neutrophil apoptosis should have increased to aid resolution of infection and inflammation". On a slightly different note Porter [3], examining transepithelial migration of lymphocytes in vitro, stated that it is widely assumed that the clearance of these cells from inflamed airway tissues involves apoptosis thus "ignoring a potentially very important exit across the bronchial epithelial barrier". This exit has been named 'luminal entry'. Analogous to the exit of cells across the venular endothelial barrier it may also be called 'transepithelial egression', 'transepithelial migration', or 'transmigrat
(RS)-Dimethylammonium 2-sec-butyl-4,6-dinitrophenolate
Carl Henrik Görbitz
Acta Crystallographica Section E , 2009, DOI: 10.1107/s1600536809038677
Abstract: The title compound, C2H8N+·C10H11N2O5 , is a highly toxic herbicide known as dinoseb. The sec-butyl group is disordered [occupancy ratio 0.828 (3):0.172 (3)], while the nitro group in the 6 position is twisted by 25° with respect to the ring plane. Pairs of –O ...H—N+—H... O– bridges between phenolic O atoms generate eight-membered hydrogen-bonded rings.
Measuring the impact of an instructional laboratory on the learning of introductory physics
Carl Wieman,N. G. Holmes
Physics , 2015,
Abstract: We have analyzed the impact of taking an associated lab course on the scores on final exam questions in two large introductory physics courses. Approximately a third of the students who completed each course also took an accompanying instructional lab course. The lab courses were fairly conventional, although they focused on supporting the mastery of a subset of the introductory physics topics covered in the associated course. Performance between students who did and did not take the lab course was compared using final exam questions from the associated courses that related to concepts from the lab courses. The population of students who took the lab in each case was somewhat different from those who did not enroll in the lab course in terms of background and major. Those differences were taken into account by normalizing their performance on the lab-related questions with scores on the exam questions that did not involve material covered in the lab. When normalized in this way, the average score on lab-related questions of the students who took the lab, in both courses, was within 1% of the score of students who did not, with an uncertainty of 2%. This result raises questions as to the effectiveness of labs at supporting mastery of physics content.
Measuring the Impact of Introductory Physics Labs on Learning
Carl Wieman,N. G. Holmes
Physics , 2015, DOI: 10.1119/1.4931717
Abstract: Our recent study showed that two lab courses, whose goals were exclusively to reinforce material developed in the lecture courses, do not have any impact on exam performance at the 1% level. In this study, we replicated this analysis with a modified version of one of these lab courses whose goals also included modeling, designing experiments, and analyzing and visualizing data. This modified course used the same sets of apparatus as the previous version, but changed the pre-lab and in-lab activities to focus on developing and testing models with data. The study evaluated the impact of these additional goals and activities. We found that they did not affect students' performance on the final exam.
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