Simultaneous recovery of bacteria and viruses from contaminated water and spinach by a filtration method

Water and leafy vegetables eaten fresh are increasingly reported as being involved in food-borne illness cases. The pathogenic agents responsible for these infections are mainly bacteria and viruses and are present in very small quantities on the contaminated food matrices. Laboratory techniques used to isolate or detect the contaminating agent differ enormously according to the type of microorganisms, generating time and economical losses. The purpose of this study was to optimize a single method which allows at the same time the recovery and concentration of these two main types of pathogenic organisms. Water and spinach samples were artificially contaminated with the feline calicivirus (FCV), rotavirus, hepatitis A virus (HAV), Escherichia coli, Listeria monocytogenes, Campylobacter jejuni and Salmonella Typhimurium. The principle behind the recovery technique is based on the use of a positively charged membrane which adsorbs both viruses and bacteria present in the water or in the rinse from the vegetables. Using conventional microbiology, PCR and RT-PCR, this filtration technique allowed a detection level superior to 10² CFU/g for S. Typhimurium, E. coli, L. monocytogenes and C. jejuni and to 10¹ PFU/g for FCV, HAV and rotavirus. This combined method can also be applied to other bacterial and viral species for the identification of the responsible agent for food-borne illnesses.     

Expression of influenza B virus hemagglutinin containing multibasic residue cleavage sites

The hemagglutinin (HA) protein of influenza B virus contains a single arginine residue at its cleavage site and the HA0 precursor is not cleaved to the HA1 and HA2 subunits by tissue culture cell-associated proteases. To investigate if an HA protein could be obtained that could be cleaved by an endogenous cellular protease, the cDNA for HA of influenza B/MD/59 virus was subjected to site-specific mutagenesis. Three HA mutant proteins were constructed, through substitution or insertion of arginine residues, that have 4, 5, or 6 basic residues at their cleavage sites. Chemical cross-linking studies indicated that all three HA cleavage site mutants could oligomerize to a trimeric species, like WT HA. The three HA cleavage site mutant proteins were efficiently transported to the cell surface and bound erythrocytes in hemadsorption assays. The mutants were cleaved at a low level to HA1 and HA2 by an endogenous host cell protease and cleavage could be increased somewhat by addition of exogenous trypsin. The fusogenic activities of the HA cleavage site mutants were assessed in comparison to the WT HA protein by determining their syncytium formation ability and by using an R18 lipid-mixing assay and a NBD-taurine aqueous-content mixing assay. While the fusion activity of the WT HA protein was dependent on exogenous trypsin to activate HA, the three HA cleavage site mutant proteins were able to induce fusion in the absence of trypsin when assayed with the R18 lipid-mixing and NBD-taurine aqueous-content mixing assays, but were unable to induce syncytium formation in either the presence or absence of exogenous trypsin. Our results suggest that while the presence of a subtilisin-like protease cleavage sequence at the influenza B virus HA1/HA2 boundary does enable some HA0 molecules to be cleaved intracellularly, it alone is not sufficient for efficient cleavage.     

The generation of random numbers that are probably prime

In this paper we make two observations on Rabin's probabilistic primality test. The first is a provocative reason why Rabin's test is so good. It turned out that a single iteration has a nonnegligible probability of failing only on composite numbers that can actually be split in expected polynomial time. Therefore, factoring would be easy if Rabin's test systematically failed with a 25% probability on each composite integer (which, of course, it does not). The second observation is more fundamental because it is not restricted to primality testing: it has consequences for the entire field of probabilistic algorithms. The failure probability when using a probabilistic algorithm for the purpose of testing some property is compared with that when using it for the purpose of obtaining a random element hopefully having this property. More specifically, we investigate the question of how reliable Rabin's test is when used to generate a random integer that is probably prime, rather than to test a specific integer for primality.Supported in part by NSERC grant A4107. Part of the research was performed while this author was at the CWI, Amsterdam.Supported in part by an NSERC Posgraduate Scholarship. Part of the research was performed while this author was at the Université de Montréal.Supported in part by an NSF grant.     

A generalization of Hellman's extension to Shannon's approach to cryptography

In his landmark 1977 paper [2], Hellman extends the Shannon theory approach to cryptography [3]. In particular, he shows that the expected number of spurious key decipherments on lengthn messages is at least 2 ^H(K)–nD –1 forany uniquely encipherable, uniquely decipherable cipher, as long as each key is equally likely and the set of meaningful cleartext messages follows a uniform distribution (whereH(K) is the key entropy andD is the redundancy of the source language). Here we show that Hellman's result holds with no restrictions on the distribution of keys and messages. We also bound from above and below the key equivocation upon seeing the ciphertext. The results are obtained through very simple purely information theoretic arguments, with no need for (explicit) counting arguments.This work was first reported at the CRYPTO 87 workshop, Santa Barbara, CA, August 1987.Supported in part by Canada NSERC Grant A4107.     

Numerical modeling of electrowetting transport processes for digital microfluidics

Electrical actuation and control of liquid droplets in Hele-Shaw cells have significant importance for microfluidics and lab-on-chip devices. Numerical modeling of complex physical phenomena like contact line dynamics, dynamic contact angles or contact angle hysteresis involved in these processes do challenge in a significant manner classical numerical approaches based on macroscopic Navier–Stokes partial differential equations. In this paper, we analyze the efficiency of a numerical lattice Boltzmann model to simulate basic transport operations of sub-millimeter liquid droplets in electrowetting actuated Hele-Shaw cells. We use a two-phase three-dimensional D3Q19 lattice Boltzmann scheme driven by a Shan–Chen-type mesoscopic potential in order to simulate the gas–liquid equilibrium state of a liquid droplet confined between two solid plates. The contact angles at the liquid–solid–gas interface are simulated by taking into consideration the interaction between fluid particles and solid nodes. The electrodes are designed as regions of tunable wettability on the bottom plate and the contact angles adjusted by changing the interaction strength of the liquid with these regions. The transport velocities obtained with this approach are compared to predictions from analytical models and very good agreement is obtained.     

Health patterns of cardiac surgery clients using home health care nursing services

The purpose of this study was to examine the health patterns of cardiac surgical patients in the home health care population and their relationships to outcomes and duration of home health care using Gordon's Functional Health Pattern framework. Home health care records of 96 cardiac surgical clients were reviewed. Admission health pattern data, reasons for admission, duration and outcomes of home care services, characteristics of hospital experience, and demographic data were analyzed. Dysfunctional health patterns were primarily in the area of activity/exercise. The most common reasons for admission were monitoring of cardiopulmonary status, wound care, and instruction on diet, medications, and cardiac regimen. The mean duration of home care was 28.8 days. Thirty percent of the sample were readmitted to the hospital. Duration of home care was shorter for those who were married and for those who reported weakness, tiredness, or fatigue as a chief complaint. Readmission to the hospital was more likely for those who had complications during their initial hospital stay and those who required at least partial assistance with bathing, dressing, feeding, or toileting. Implications for practice and research are discussed.     

A computer program for fitting multimodal probability density functions

A FORTRAN IV program is described, which may be run interactively with tutorial assistance or in batch and which allows a user to selectively fit any of seven probability density functions (p.d.f.'s) or a combination of the p.d.f.'s to a unimodal or multimodal histogram of empirical data. A "best-fit", uni- or multimodal p.d.f., which may be obtained by a method of nonlinear least squares or a generated p.d.f. may be displayed on a Tektronix 4010 terminal as a continuous curve against the background of a bar, square wave, symbol or point-plot histogram. The following, supportive statistical information is also displayed: (1) Kolmogorov-Smirnov probability of goodness of fit, (2) mean square error, (3) correlation coefficient, and (4) parameter estimates. The resident driver program and six overlayable segments have been implemented on a Digital Equipment Corporation LAB-11 minicomputer (PDP-11/20).     

Experimental quantum cryptography

We describe results from an apparatus and protocol designed to implement quantum key distribution, by which two users, who share no secret information initially: (1) exchange a random quantum transmission, consisting of very faint flashes of polarized light; (2) by subsequent public discussion of the sent and received versions of this transmission estimate the extent of eavesdropping that might have taken place on it, and finally (3) if this estimate is small enough, distill from the sent and received versions a smaller body of shared random information, which is certifiably secret in the sense that any third party's expected information on it is an exponentially small fraction of one bit. Because the system depends on the uncertainty principle of quantum physics, instead of the usual mathematical assumptions such as the difficulty of factoring, it remains secure against an adversary with unlimited computing power.This paper was accepted prior to the present Editor-in-Chief taking responsibility. A preliminary version of this paper was presented at Eurocrypt '90, May 21–24, Århus, Denmark, and has appeared in the proceedings, pp. 253–265. François Bessette was supported in part by an NSERC Postgraduate Scholarship. Gilles Brassard was supported in part by Canada's NSERC. This work was performed while John Smolin was visiting IBM Research.     

Self-priming of liquids in capillary autonomous microfluidic systems

We present a numerical approach to the capillary rise dynamics in microfluidic channels of complex 3D geometries. In order to optimize the delivery of specific biological fluids to target regions in microfluidic capillary autonomous systems (CAS), we analyze self-priming of liquid water into a microfluidic device consisting of a microfluidic channel that feeds a rectangular microfluidic cavity trough an appropriately designed micro-chamber. The target performance criteria in our optimization are (1) fast and complete wetting of the cavity bottom while (2) minimizing the probability of trapping air bubble in the device. The numerical model is based on the lattice Boltzmann method (LBM) and a three-dimensional single-component multiple-phase (SCMP) scheme. By using a parallel implementation of this algorithm, we investigate the physical processes related to the invasion of the liquid–gas interfaces in rectangular cavities at different liquid–solid contact angle and shapes of the transition micro-chamber. The numerical results has successfully captured important qualitative and some key quantitative effects of the liquid–solid contact angle, the roughness of the cavity edges, the depth of the holes and shape of the micro-chambers. Moreover, we present and validate experimentally simple geometrical optimizations of the microfluidic device that ensure the complete filling the microfluidic cavity with liquid. Critical parameters related to the overall priming time of the device are presented as well.