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In the present work, a three-dimension (3-D) model of polymer electrolyte fuel cells (PEFCs) is employed to investigate the complex, non-isothermal, two-phase flow in the gas diffusion layer (GDL). Phase change in gas flow channels is explained, and a simplified approach accounting for phase change is incorporated into the fuel cell model. It is found that the liquid water contours in the GDL are similar along flow channels when the channels are subject to two-phase flow. Analysis is performed on a dimensionless parameter Da0 introduced in our previous paper [Y. Wang and K. S. Chen, Chemical Engineering Science 66 (2011) 3557–3567] and the parameter is further evaluated in a realistic fuel cell. We found that the GDL's liquid water (or liquid-free) region is determined by the Da0 number which lumps several parameters, including the thermal conductivity and operating temperature. By adjusting these factors, a liquid-free GDL zone can be created even though the channel stream is two-phase flow. Such a liquid-free zone is adjacent to the two-phase region, benefiting local water management, namely avoiding both severe flooding and dryness.

In the present work, a three-dimension (3-D) model of polymer electrolyte fuel cells (PEFCs) is employed to investigate the complex, non-isothermal, two-phase flow in the gas diffusion layer (GDL). Phase change in gas flow channels is explained, and a simplified approach accounting for phase change is incorporated into the fuel cell model. It is found that the liquid water contours in the GDL are similar along flow channels when the channels are subject to two-phase flow. Analysis is performed on a dimensionless parameter Da0 introduced in our previous paper [Y. Wang and K. S. Chen, Chemical Engineering Science 66 (2011) 3557–3567] and the parameter is further evaluated in a realistic fuel cell. We found that the GDL's liquid water (or liquid-free) region is determined by the Da0 number which lumps several parameters, including the thermal conductivity and operating temperature. By adjusting these factors, a liquid-free GDL zone can be created even though the channel stream is two-phase flow. Such a liquid-free zone is adjacent to the two-phase region, benefiting local water management, namely avoiding both severe flooding and dryness.

BACKGROUND: The universal presence of a gene (SMN2) nearly identical to the mutated SMN1 gene responsible for Spinal Muscular Atrophy (SMA) has proved an enticing incentive to therapeutics development. Early disappointments from putative SMN-enhancing agent clinical trials have increased interest in improving the assessment of SMN expression in blood as an early "biomarker" of treatment effect. METHODS: A cross-sectional, single visit, multi-center design assessed SMN transcript and protein in 108 SMA and 22 age and gender-matched healthy control subjects, while motor function was assessed by the Modified Hammersmith Functional Motor Scale (MHFMS). Enrollment selectively targeted a broad range of SMA subjects that would permit maximum power to distinguish the relative influence of SMN2 copy number, SMA type, present motor function, and age. RESULTS: SMN2 copy number and levels of full-length SMN2 transcripts correlated with SMA type, and like SMN protein levels, were lower in SMA subjects compared to controls. No measure of SMN expression correlated strongly with MHFMS. A key finding is that SMN2 copy number, levels of transcript and protein showed no correlation with each other. CONCLUSION: This is a prospective study that uses the most advanced techniques of SMN transcript and protein measurement in a large selectively-recruited cohort of individuals with SMA. There is a relationship between measures of SMN expression in blood and SMA type, but not a strong correlation to motor function as measured by the MHFMS. Low SMN transcript and protein levels in the SMA subjects relative to controls suggest that these measures of SMN in accessible tissues may be amenable to an "early look" for target engagement in clinical trials of putative SMN-enhancing agents. Full length SMN transcript abundance may provide insight into the molecular mechanism of phenotypic variation as a function of SMN2 copy number. TRIAL REGISTRY: Clinicaltrials.gov NCT00756821.

This paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da→0, the fuel cell is subjected to single-phase operation; while as Da→ we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da0: when Da0>1 the entire cathode GDL-CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da0<1. The latter scenario is the concept that this paper proposes for improving fuel cell water management: the consequent co-occurrence of single- and two-phase flows in the in-plane direction at Da0<1 is beneficial to avoid severe dryout and flooding. A two-phase transport model, describing the water and heat transport on the PEFC cathode side, is employed to perform a two-dimensional numerical study. Detailed liquid and temperature distributions are displayed. Simulation predictions are in reasonably good agreement with the dimensionless-group analysis. © 2011 Elsevier Ltd.

This paper explores the through-/in-plane characteristics of water transport in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). Theoretical analysis is performed on the non-isothermal two-phase flow under flow channels. A dimensionless group Da (Damkohler number for PEFC operation), defined as the ratio of water generation rate to water vapor-phase removal rate, is formulated to characterize the flow regimes in a PEFC. This group, lumping geometrical parameters and physical properties, compares the water vapor-phase removal capability (via water diffusion and holding capacity) with the rate of water production by the oxygen reduction reaction. We find that this dimensionless group can be used to characterize the non-isothermal, two-phase phenomena: when Da→0, the fuel cell is subjected to single-phase operation; while as Da→ we have full two-phase operation. A more precise expression is explored for the dimensionless group at the channel central line, i.e. Da0: when Da0>1 the entire cathode GDL-CL (catalyst layer) interface is in two-phase region, whereas part of the interface is free of liquid water for Da0<1. The latter scenario is the concept that this paper proposes for improving fuel cell water management: the consequent co-occurrence of single- and two-phase flows in the in-plane direction at Da0<1 is beneficial to avoid severe dryout and flooding. A two-phase transport model, describing the water and heat transport on the PEFC cathode side, is employed to perform a two-dimensional numerical study. Detailed liquid and temperature distributions are displayed. Simulation predictions are in reasonably good agreement with the dimensionless-group analysis. © 2011 Elsevier Ltd.

A multidimensional mathematical model is presented for simulating the coupled phenomena of gaseous fuel/reactant flows, species (including liquid water) transport, heat transfer, hydrogen oxidation, and oxygen reduction reactions in a polymer electrolyte fuel cell (PEFC). The present work focuses on elucidating water distribution in the through-plane direction, in particular across the membrane electrode assembly (MEA) and gas diffusion layer (GDL). Two-dimensional model predictions are computed numerically and compared with available experimental data from neutron radiography or imaging. Using the same set of model parameters, reasonably good agreements are obtained quantitatively between the computed water profile in the MEA-GDL component and the neutron-imaging data reported by two separate research groups, and qualitatively between model prediction and the data from another (third) group. Case-study simulations are carried out for PEFC operation at various temperatures, relative humidities, and current densities. It is found that liquid-water content is lower at higher cell temperatures due to greater water evaporation and stronger water diffusion in the vapor phase, as expected. Without strong water diffusion in the vapor phase, the liquid-water profiles are found to increase with current density in the cathode GDL but indicate a complex trend in the anode. Effect of varying GDL thermal conductivity on water distribution is also examined. © 2010 The Electrochemical Society.

A multidimensional mathematical model is presented for simulating the coupled phenomena of gaseous fuel/reactant flows, species (including liquid water) transport, heat transfer, hydrogen oxidation, and oxygen reduction reactions in a polymer electrolyte fuel cell (PEFC). The present work focuses on elucidating water distribution in the through-plane direction, in particular across the membrane electrode assembly (MEA) and gas diffusion layer (GDL). Two-dimensional model predictions are computed numerically and compared with available experimental data from neutron radiography or imaging. Using the same set of model parameters, reasonably good agreements are obtained quantitatively between the computed water profile in the MEA-GDL component and the neutron-imaging data reported by two separate research groups, and qualitatively between model prediction and the data from another (third) group. Case-study simulations are carried out for PEFC operation at various temperatures, relative humidities, and current densities. It is found that liquid-water content is lower at higher cell temperatures due to greater water evaporation and stronger water diffusion in the vapor phase, as expected. Without strong water diffusion in the vapor phase, the liquid-water profiles are found to increase with current density in the cathode GDL but indicate a complex trend in the anode. Effect of varying GDL thermal conductivity on water distribution is also examined. © 2010 The Electrochemical Society.

Mobile wireless services have witnessed phenomenal growth recently. Meanwhile, multicasting has played an increasingly important role in many conventional and emerging applications, such as teleconferencing and distributed games. Although efforts to support multicasting over fixed wireline networks (the Internet and ATM) have been considerable, multicasting over mobile wireless systems, which involves a new set of challenges, has seldom been addressed. This inequality results primarily from the movement of mobile users, which mandates that any multicasting configuration be highly dynamic. For example, the existing multicast technology in fixed networks focuses mainly on minimizing the cost of multicast trees with a delay constraint through join and leave operations, an approach that is not suitable for mobile wireless systems because of the provisioning of handoff. Additionally, the multicast connection tree constructed may become inefficient due to the lack of efficient regimes when a new (existing) mobile user initially joins (finally leaves) the group. Following the movement of roaming members, the tree may thus expand and consume excessive resources. Consequently, how to provide efficient support for multicasting over mobile wireless networks merits careful examination. This study considers the multicasting problem in the context of generic wireless systems. Specifically, a novel Constrained Tree Migration Scheme (CTMS) is created to support multicast services in mobile wireless networks. The salient features of the novel CTMS include: 1) automatically recognizing the inefficiency of the multicast trees, then migrating them to better ones, while maintaining the QoS guarantees specified by mobile users; 2) conserving network resources by maintaining a low-cost multicast tree, thus accommodating more users; 3) operating efficiently in a truly distributed manner through event driven and diffusing computations, thus increasing the degree of scalability; 4) synchroni

Mobile wireless services have witnessed phenomenal growth recently. Meanwhile, multicasting has played an increasingly important role in many conventional and emerging applications, such as teleconferencing and distributed games. Although efforts to support multicasting over fixed wireline networks (the Internet and ATM) have been considerable, multicasting over mobile wireless systems, which involves a new set of challenges, has seldom been addressed. This inequality results primarily from the movement of mobile users, which mandates that any multicasting configuration be highly dynamic. For example, the existing multicast technology in fixed networks focuses mainly on minimizing the cost of multicast trees with a delay constraint through join and leave operations, an approach that is not suitable for mobile wireless systems because of the provisioning of handoff. Additionally, the multicast connection tree constructed may become inefficient due to the lack of efficient regimes when a new (existing) mobile user initially joins (finally leaves) the group. Following the movement of roaming members, the tree may thus expand and consume excessive resources. Consequently, how to provide efficient support for multicasting over mobile wireless networks merits careful examination. This study considers the multicasting problem in the context of generic wireless systems. Specifically, a novel Constrained Tree Migration Scheme (CTMS) is created to support multicast services in mobile wireless networks. The salient features of the novel CTMS include: 1) automatically recognizing the inefficiency of the multicast trees, then migrating them to better ones, while maintaining the QoS guarantees specified by mobile users; 2) conserving network resources by maintaining a low-cost multicast tree, thus accommodating more users; 3) operating efficiently in a truly distributed manner through event driven and diffusing computations, thus increasing the degree of scalability; 4) synchroni

Mobile wireless services have witnessed phenomenal growth recently. Meanwhile, multicasting has played an increasingly important role in many conventional and emerging applications, such as teleconferencing and distributed games. Although efforts to support multicasting over fixed wireline networks (the Internet and ATM) have been considerable, multicasting over mobile wireless systems, which involves a new set of challenges, has seldom been addressed. This inequality results primarily from the movement of mobile users, which mandates that any multicasting configuration be highly dynamic. For example, the existing multicast technology in fixed networks focuses mainly on minimizing the cost of multicast trees with a delay constraint through join and leave operations, an approach that is not suitable for mobile wireless systems because of the provisioning of handoff. Additionally, the multicast connection tree constructed may become inefficient due to the lack of efficient regimes when a new (existing) mobile user initially joins (finally leaves) the group. Following the movement of roaming members, the tree may thus expand and consume excessive resources. Consequently, how to provide efficient support for multicasting over mobile wireless networks merits careful examination. This study considers the multicasting problem in the context of generic wireless systems. Specifically, a novel Constrained Tree Migration Scheme (CTMS) is created to support multicast services in mobile wireless networks. The salient features of the novel CTMS include: 1) automatically recognizing the inefficiency of the multicast trees, then migrating them to better ones, while maintaining the QoS guarantees specified by mobile users; 2) conserving network resources by maintaining a low-cost multicast tree, thus accommodating more users; 3) operating efficiently in a truly distributed manner through event driven and diffusing computations, thus increasing the degree of scalability; 4) synchroni

Recombination between repeated sequences at various loci of the human genome are known to give rise to DNA rearrangements associated with many genetic disorders. Perhaps the most extensively characterized genomic region prone to rearrangement is 17p12, which is associated with the peripheral neuropathies, hereditary neuropathy with liability to pressure palsies (HNPP) and Charcot-Marie-Tooth disease type 1A (CMT1A;ref. 2). Homologous recombination between 24-kb flanking repeats, termed CMT1A-REPs, results in a 1.5-Mb deletion that is associated with HNPP, and the reciprocal duplication product is associated with CMT1A (ref. 2). Smith-Magenis syndrome (SMS) is a multiple congenital anomalies, mental retardation syndrome associated with a chromosome 17 microdeletion, del(17)(p11.2p11.2) (ref. 3,4). Most patients (>90%) carry deletions of the same genetic markers and define a common deletion. We report seven unrelated patients with de novo duplications of the same region deleted in SMS. A unique junction fragment, of the same apparent size, was identified in each patient by pulsed field gel electrophoresis (PFGE). Further molecular analyses suggest that the de novo17p11.2 duplication is preferentially paternal in origin, arises from unequal crossing over due to homologous recombination between flanking repeat gene clusters and probably represents the reciprocal recombination product of the SMS deletion. The clinical phenotype resulting from duplication [dup(17)(p11.2p11.2)] is milder than that associated with deficiency of this genomic region. This mechanism of reciprocal deletion and duplication via homologous recombination may not only pertain to the 17p11.2 region, but may also be common to other regions of the genome where interstitial microdeletion syndromes have been defined.

Recombination between repeated sequences at various loci of the human genome are known to give rise to DNA rearrangements associated with many genetic disorders. Perhaps the most extensively characterized genomic region prone to rearrangement is 17p12, which is associated with the peripheral neuropathies, hereditary neuropathy with liability to pressure palsies (HNPP) and Charcot-Marie-Tooth disease type 1A (CMT1A;ref. 2). Homologous recombination between 24-kb flanking repeats, termed CMT1A-REPs, results in a 1.5-Mb deletion that is associated with HNPP, and the reciprocal duplication product is associated with CMT1A (ref. 2). Smith-Magenis syndrome (SMS) is a multiple congenital anomalies, mental retardation syndrome associated with a chromosome 17 microdeletion, del(17)(p11.2p11.2) (ref. 3,4). Most patients (>90%) carry deletions of the same genetic markers and define a common deletion. We report seven unrelated patients with de novo duplications of the same region deleted in SMS. A unique junction fragment, of the same apparent size, was identified in each patient by pulsed field gel electrophoresis (PFGE). Further molecular analyses suggest that the de novo17p11.2 duplication is preferentially paternal in origin, arises from unequal crossing over due to homologous recombination between flanking repeat gene clusters and probably represents the reciprocal recombination product of the SMS deletion. The clinical phenotype resulting from duplication [dup(17)(p11.2p11.2)] is milder than that associated with deficiency of this genomic region. This mechanism of reciprocal deletion and duplication via homologous recombination may not only pertain to the 17p11.2 region, but may also be common to other regions of the genome where interstitial microdeletion syndromes have been defined.