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Deep-space network channels are characterized "in part" by asymmetric channel rates. The effect of the asymmetric channel rates is that the slow acknowledgement (ACK) channel cannot effectively support transmission of the ACK segments generated at the data receiver. Increment of data block size and extension of the retransmission timeout (RTO) timer are widely used transmission mechanisms for eliminating the effect of highly channel-rate asymmetry. The aggregate custody signal (ACS) is recently proposed to resolve the effect of asymmetric channel rates in deep-space networks. In this article, these three acknowledgment mechanisms are studied, with a focus on a comparison of their effectiveness evaluation over highly asymmetric deep-space network channels accompanied by data loss. The study is conducted through realistic file delivery via an experimental testbed infrastructure. It is found that the ACS mechanism shows significant performance advantages over other two mechanisms for both the "normalized" goodput and total data amount in successful file delivery. In particular, the ACS mechanism makes it a better choice to operate with small data bundles without increasing the RTO timer length. [ABSTRACT FROM AUTHOR]

Bundle protocol (BP) is the core protocol of delay/disruption-tolerant networking, which has been recognized as the only candidate networking technology that approaches the level of maturity required for deep-space mission communications. BP is intended to establish an overlay network for reliable data transfer over highly unreliable space links. A hybrid reliability strategy based on combining "proactive" retransmission and "reactive" retransmission of BP bundles is presented in this article as a means of achieving highly reliable file/data delivery in deep-space communication networks. Available electrical power on spacecraft is widely recognized as a scarce resource, especially for spacecraft in deep space where energy consumption is an important consideration for communications. In this article, the hybrid bundle retransmission approach is studied by means of a file transfer experiment over a PC-based testbed. The study focuses on variation in the transmission overhead and energy consumption of BP as a function of file size and retransmission timeout interval length. [ABSTRACT FROM AUTHOR]

Developed as the main protocol of delay/disruption-tolerant networking (DTN) for space, bundle protocol (BP) is intended to establish an overlay network for reliable data delivery in a heterogeneous networking environment. The effect of a link disruption on reliable data transmission of BP is currently under study. In this paper, a study of the effect of link disruption on BP's reliable data delivery in deep-space vehicle communications, from spatial and temporal perspectives, is presented employing both analytical and experimental methods. The effect is modeled in various transmission cases by considering the physical distance the bundle has traversed when the link disruption starts and ends, the duration of link disruption in time, and the physical span of the link disruption. The models are built to quantify the number of transmission attempts that fail due to link disruption, the total number of transmission attempts, bundle delivery time, and transmission goodput performance for successful bundle delivery in presence of a link disruption. The models are validated by realistic bundle delivery over a PC-based experimental testbed. The validation indicates that the analytical models predict the transmission performance of BP in presence of random link disruption in various aspects of successful bundle delivery. [ABSTRACT FROM AUTHOR]

In order to reduce the chattering and phase shift, this article proposes an enhanced sliding mode observer (SMO) for the sensorless control of permanent magnet synchronous motor (PMSM). In the conventional SMO, a low-pass filter (LPF) is commonly employed to extract the back electromotive forces (EMFs) from the sliding mode switching function, which brings the phase shift and degrades the precision of position and speed estimations. In this article, a frequency-adaptive complex-coefficient filter (FACCF) is adopted to replace the LPF. Since the FACCF has no phase shift and amplitude attenuation at the central frequency, it can be used to extract the EMFs without distortion while the chattering can also be suppressed. For an easy parameter design, the normalized phase-locked loop is used to obtain accurately the position and speed estimations. The experiments are carried out on a 3-kW PMSM drive, and the results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The rapid detection of Salmonella in ground meat requires that living microorganisms be brought to levels detectable by PCR, immunoassays, or similar techniques within 8 h. Previously, we employed microfiltration using hollow fiber membranes to rapidly process and concentrate viable bacteria in food extracts through a combination of enzyme treatment and prefiltration in order to prevent blockage or fouling of the hollow fiber membranes. However, scanning electron microscopy and particle size analysis of enzyme hydrolysates showed that enzyme treatment followed by filtration caused submicron particles to form and be trapped within the prefiltration media, which in turn, retained about 80% of the bacteria. Filtering prior to enzyme treatment resulted in formation of a filter cake consisting of protein particles retained on the surface of the filter, while facilitating passage of the much smaller microorganisms through the filter, separating them from particulates. Subsequent enzyme treatment of the filtrate resulted in an extract that was microfiltered in less than an hour, while concentrating viable microorganisms in the extract by 500×. An inoculum of Salmonella enterica cells into turkey burger containing of 1-20 CFU/mL, consisting of spiked cells plus cells already present in the turkey burger sample, was rapidly brought to levels detectable by conventional PCR and BAX® PCR assays. The entire procedure from sample processing to detection of Salmonella enterica was achieved in less than 8 h. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:687-695, 2017 [ABSTRACT FROM AUTHOR]

The antimicrobial action of porous CuO microspheres (μCuO), Ag nanoparticles (nAg), and bimetallic porous CuO microspheres decorated with Ag nanoparticles (μCuO/nAg) was evaluated against surrogate microorganisms representative of pathogens commonly implicated in foodborne and healthcare-associated human infections. This work addressed the Gram-negative bacteria E. coli (Escherichia coli O157:H7-GFP B6-914), Salmonella (Salmonella enterica serovar enteritidis phage-type PT21), and the Gram-positive bacteria Listeria (Listeria innocua), as well as environmental microorganisms derived from local river water. Compared to particles composed only of CuO or Ag, the bimetallic porous μCuO/nAg particle exhibits enhanced antimicrobial efficacy. The antimicrobial action of bimetallic porous μCuO/nAg particles is dose-dependent, with 50 μg/mL particle concentration completely inhibiting the growth of both the Gram-negative (Salmonella) and the Gram-positive (Listeria) bacteria after 6 h. To assess the mechanism of antimicrobial action, the changes in surface morphologies of bacteria treated with the particles were observed using scanning electron microscopy. In the case of the Gram-negative bacteria, the bacterial cell membrane is damaged, likely due to the release of metal ions from the particles; however, particle-induced cell membrane damage is not observed for Gram-positive bacteria. Collectively, results from this work shed further light on possible mechanisms of antimicrobial action of micro-/nanoparticles and highlight the potential for bimetallic particle-based inhibition of microbial infections.

This paper reports an approach to enable rapid concentration and recovery of bacterial cells from aqueous chicken homogenates as a preanalytical step of detection. This approach includes biochemical pretreatment and prefiltration of food samples and development of an automated cell concentration instrument based on cross-flow microfiltration. A polysulfone hollow-fiber membrane module having a nominal pore size of 0.2 μm constitutes the core of the cell concentration instrument. The aqueous chicken homogenate samples were circulated within the cross-flow system achieving 500- to 1,000-fold concentration of inoculated Salmonella enterica serovar Enteritidis and naturally occurring microbiota with 70% recovery of viable cells as determined by plate counting and quantitative PCR (qPCR) within 35 to 45 min. These steps enabled 10 CFU/ml microorganisms in chicken homogenates or 10(2) CFU/g chicken to be quantified. Cleaning and sterilizing the instrument and membrane module by stepwise hydraulic and chemical cleaning (sodium hydroxide and ethanol) enabled reuse of the membrane 15 times before replacement. This approach begins to address the critical need for the food industry for detecting food pathogens within 6 h or less.