Minimal Buffering Research Articles

Amino acid assisted Ca2+ leaching-CO2 mineralization: Thermodynamic equilibrium analysis and experimental investigation

An amino acid-mediated Ca2+ leaching-CO2 mineralization process was proposed to address the challenges associated with slow kinetics and extensive consumption of exogenous reagents in CO2 mineralization. While the underlying reaction mechanism between amino acid and alkaline minerals/metals remains unclear, this study explored the interactions between amino acid-species and Ca-bearing minerals/Ca2+ by investigating the evolution of active compounds from the perspectives of thermodynamic equilibrium analysis and experimental study. Thermodynamic equilibrium analysis showed that the active Ca-bearing minerals of coal fly ash (CFA) varied in the systems of ammonium salt, acid, and amino acid, e.g., the active phases in glycine were portlandite (Ca(OH)2), lime (CaO), and gehlenite (2CaO*Al2O3*SiO2). High Ca2+ concentrations of 0.26 M, 0.14 M, and 0.1 M can be achieved after 3 min of leaching assisted by amino acids of Glycine (Gly), L-Alanine (Ala), and L-Arginine (Arg), respectively, which implied the kinetics and thermodynamical feasibility. This phenomenon was demonstrated to relate to the fact that Gly and Ala had minimal pH buffering capacity in the early leaching stage. The deprotonated forms of Gly and Ala with a higher affinity with Ca2+ increased from 0.03 % and 0.04 % to 33.9 % and 12.88 %, respectively, thereby promoting Ca2+ leaching. The Ca2+ utilization efficiencies from CFA were 26.45 %, 15.0 %, and 13.3 % for Gly, Ala, and Arg, respectively. Gly achieved the best CaCO3 yield of 114.8 g/kg, due to the combined effects of Gly’s buffering capacity and strong chelation effect for Ca2+, which drove forward the dissolution of the active phase and precipitation of CaCO3.

A Literature Review on Implementation of Lean Tools in Industries and Enterprises

In today's competitive environment, lean manufacturing becomes necessary across all industries. Lean production is a contemporary production technique of the new millennium. Lean manufacturing has varied synonyms just as lean management, lean production. It provides an extensive approach for decreasing the flow of non-value-added activities. Lean manufacturing is an excellent philosophy to minimize the period amongst client orders and supplies are ready for delivery through eradicating waste. Waste (Muda) is implicit like any process or activity that would not be adding value to the finished product or services. Waste is a severe problem emerging in the manufacturing industries; it causes non-value-added steps which do not expedite outstanding products and services. Waste is minimized with the aid of lean manufacturing. It is an integrated system that entails a minimal buffering cost for services offered and manufactured goods. The present research studies in the domain of Lean are examined to comprehend the execution level of several lean tools, benefits of implementation, and obstacles during the execution of Lean are also scrutinized in the reviewing. Several benefits and potential barriers that occur while implementing the lean culture in various organizations have been identified and listed in this paper.

Multiple geochemical factors may cause iodine and selenium deficiency in Gilgit-Baltistan, Pakistan

Deficiencies of the micronutrients iodine and selenium are particularly prevalent where populations consume local agricultural produce grown on soils with low iodine and selenium availability. This study focussed on such an area, Gilgit-Baltistan in Pakistan, through a geochemical survey of iodine and selenium fractionation and speciation in irrigation water and arable soil. Iodine and selenium concentrations in water ranged from 0.01–1.79 µg L−1 to 0.016–2.09 µg L−1, respectively, which are smaller than levels reported in similar mountainous areas in other parts of the world. Iodate and selenate were the dominant inorganic species in all water samples. Average concentrations of iodine and selenium in soil were 685 µg kg−1 and 209 µg kg−1, respectively, much lower than global averages of 2600 and 400 µg kg−1, respectively. The ‘reactive’ fractions (‘soluble’ and ‘adsorbed’) of iodine and selenium accounted for < 7% and < 5% of their total concentrations in soil. More than 90% of reactive iodine was organic; iodide was the main inorganic species. By contrast, 66.9 and 39.7% of ‘soluble’ and ‘adsorbed’ selenium, respectively, were present as organic species; inorganic selenium was mainly selenite. Very low distribution coefficients (kd = adsorbed/soluble; L kg−1) for iodine (1.07) and selenium (1.27) suggested minimal buffering of available iodine and selenium against leaching losses and plant uptake. These geochemical characteristics suggest low availability of iodine and selenium in Gilgit-Baltistan, which may be reflected in locally grown crops. However, further investigation is required to ascertain the status of iodine and selenium in the Gilgit-Baltistan food supply and population.

Local Postsynaptic Signaling on Slow Time Scales in Reciprocal Olfactory Bulb Granule Cell Spines Matches Asynchronous Release.

In the vertebrate olfactory bulb (OB), axonless granule cells (GC) mediate self- and lateral inhibitory interactions between mitral/tufted cells via reciprocal dendrodendritic synapses. Locally triggered release of GABA from the large reciprocal GC spines occurs on both fast and slow time scales, possibly enabling parallel processing during olfactory perception. Here we investigate local mechanisms for asynchronous spine output. To reveal the temporal and spatial characteristics of postsynaptic ion transients, we imaged spine and adjacent dendrite Ca2 +- and Na+-signals with minimal exogenous buffering by the respective fluorescent indicator dyes upon two-photon uncaging of DNI-glutamate in OB slices from juvenile rats. Both postsynaptic fluorescence signals decayed slowly, with average half durations in the spine head of t1/2_Δ[Ca2 +]i ∼500 ms and t1/2_Δ[Na+]i ∼1,000 ms. We also analyzed the kinetics of already existing data of postsynaptic spine Ca2 +-signals in response to glomerular stimulation in OB slices from adult mice, either WT or animals with partial GC glutamate receptor deletions (NMDAR: GluN1 subunit; AMPAR: GluA2 subunit). In a large subset of spines the fluorescence signal had a protracted rise time (average time to peak ∼400 ms, range 20 to >1,000 ms). This slow rise was independent of Ca2 + entry via NMDARs, since similarly slow signals occurred in ΔGluN1 GCs. Additional Ca2 + entry in ΔGluA2 GCs (with AMPARs rendered Ca2 +-permeable), however, resulted in larger ΔF/Fs that rose yet more slowly. Thus GC spines appear to dispose of several local mechanisms to promote asynchronous GABA release, which are reflected in the time course of mitral/tufted cell recurrent inhibition.

The effects of elevated temperature and PCO2 on the energetics and haemolymph pH homeostasis of juveniles of the European lobster, Homarus gammarus.

Regulation of extracellular acid-base balance, while maintaining energy metabolism, is recognised as an important aspect when defining an organism's sensitivity to environmental changes. This study investigated the haemolymph buffering capacity and energy metabolism (oxygen consumption, haemolymph [l-lactate] and [protein]) in early benthic juveniles (carapace length <40 mm) of the European lobster, Homarus gammarus, exposed to elevated temperature and PCO2 At 13°C, H. gammarus juveniles were able to fully compensate for acid-base disturbances caused by the exposure to elevated seawater PCO2 at levels associated with ocean acidification and carbon dioxide capture and storage (CCS) leakage scenarios, via haemolymph [HCO3-] regulation. However, metabolic rate remained constant and food consumption decreased under elevated PCO2 , indicating reduced energy availability. Juveniles at 17°C showed no ability to actively compensate haemolymph pH, resulting in decreased haemolymph pH particularly under CCS conditions. Early benthic juvenile lobsters at 17°C were not able to increase energy intake to offset increased energy demand and therefore appear to be unable to respond to acid-base disturbances due to increased PCO2at elevated temperature. Analysis of haemolymph metabolites suggests that, even under control conditions, juveniles were energetically limited. They exhibited high haemolymph [l-lactate], indicating recourse to anaerobic metabolism. Low haemolymph [protein] was linked to minimal non-bicarbonate buffering and reduced oxygen transport capacity. We discuss these results in the context of potential impacts of ongoing ocean change and CCS leakage scenarios on the development of juvenile H. gammarus and future lobster populations and stocks.

Xylenol orange-based loop-mediated DNA isothermal amplification for sensitive naked-eye detection of Escherichia coli

Loop-mediated isothermal amplification (LAMP) can amplify DNA specifically and sensitively. Under minimal buffering conditions, it produces hydrogen ions that lower the pH of the solution upon DNA amplification. This characteristic was applied to visually detect amplified DNA of Escherichia coli through the use of Xylenol Orange, a pH-dependent dye. Under the optimal conditions, 120 min at 63 °C, the Xylenol orange-dependent colorimetric LAMP revealed a detection limit as low as 1 CFU, namely 100,000 times more sensitive than typical multiplex PCR, and showed no cross-reactions with other foodborne pathogens. The colorimetric assay was successfully exploited to detect E. coli contaminations in milk samples, showing high reliability and the same high sensitivity with naked-eye readout. Together with robustness, simplicity, and visual detectability of amplification, this assay can serve as an alternative tool to PCR for detecting E. coli, which is suitable for both laboratory and on-field applications.

Does the moon influence sleep in small-scale societies?

ObjectivesThe lunar cycle is expected to influence sleep-wake patterns in human populations that have greater exposure to the environment, as might be found in forager populations that experience few environmental buffers. We investigated this “moonlight” hypothesis in two African populations: one composed of hunter-gatherers (with minimal environmental buffering) and the other rural agriculturalists (with low-to-moderate environmental buffering). SettingResearch was conducted on Hadza hunter-gatherers from the Sengele community near Lake Eyasi in northern Tanzania and in Mandena, Madagascar, in a rural community of approximately 4000 farmers. ParticipantsThirty-one adult Hadza and 21 Malagasy adults were recruited. MeasurementsWe used the CamNtech Motionwatch 8 actigraph and generated data on an epoch-by-epoch, 1-minute basis. ResultsIn general support of the moonlight hypothesis, we uncovered an association between sleep-wake patterns and lunar cycle (ie., moonlight) for Hadza hunter-gatherers. However, the direction of the effect was opposite to what we predicted: as the potential for exposure to moonlight increased, activity generally shifted to a pattern of less nighttime activity and greater daytime activity. No significant effects were found in the Malagasy agriculturalists. ConclusionsThe proposal that human behaviors are linked with moon phase is a popular belief that persists despite the absence of consistent evidence. We provide the first direct evidence that lunar cycle is linked to sleep-wake pattern in a hunter-gatherer society, suggesting that moonlight does not inhibit sleep-wake patterns in the ways that electric lighting does.

Development of a colorimetric RT-LAMP amplification assay adapted to an early and easy detection of Dengue virus

Background: Dengue viruses (DENV) produce one of the most important emerging viral diseases around the world. This mosquito-borne disease has the greater impact in tropical/subtropical areas, causing symptoms ranging from acute, self-limiting febrile illness, dengue fever, to severe dengue hemorrhagic fever to dengue shock syndrome. The infection is caused by 4 distinct, but closely related, serotypes (DENV-1, DENV-2, DENV-3 and DENV-4). There are neither specific antiviral drugs nor approved vaccines; then, an early detection is a crucial step for proper patient management, lowing fatality rates, and for preventing the spread of the disease. The aim of this work was to develop a simplified test for DENV detection in early stages (during the febrile period of the infection), identifying the serotype involved. Methods & Materials: We developed and evaluated a colorimetric reverse transcriptase loop-mediated isothermal amplification assay (ColorRT- LAMP), an alternative method of polymerase chain reaction (PCR) that, as it works at a fixed temperature, not require thermocyclers and, also, can be performed in short times, showing accurate and reliable results. The complete reaction was performed in one step in a single tube by mixing primers, reverse-transcriptase and DNA polymerase together with the tested samples (RNA genomes from the international references of Dengue serotypes). Ranges of temperature and time were evaluated, selecting 65 ∘C for 60 min as the best reaction options. The read out of the test was defined as a color change -visible to a naked eye-, by the addition of a visible pH indicator dye, the neutral red dye, prior to the amplification; this pH indicator changes its color as a result of the amplification performed under minimal buffering conditions. Results: Here we described the achievement of an early and easy DENV detection test. The results showed that our ColorRT- LAMP test is highly sensitive, more than quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and highly specific, differentiating between the four serotypes and not showing cross reaction with another closely related arbovirus (Zika). Conclusion: Here we described the development of a simple ColorRT- LAMP test that could be used as a powerful tool for an early, easy, and sensible detection of Dengue disease.

Mineralogical controls on porosity and water chemistry during O2-SO2-CO2 reaction of CO2 storage reservoir and cap-rock core

Reservoir and cap-rock core samples with variable lithology's representative of siliciclastic reservoirs used for CO2 storage have been characterized and reacted at reservoir conditions with an impure CO2 stream and low salinity brine. Cores from a target CO2 storage site in Queensland, Australia were tested. Mineralogical controls on the resulting changes to porosity and water chemistry have been identified. The tested siliciclastic reservoir core samples can be grouped generally into three responses to impure CO2-brine reaction, dependent on mineralogy. The mineralogically clean quartzose reservoir cores had high porosities, with negligible change after reaction, in resolvable porosity or mineralogy, calculated using X-ray micro computed tomography and QEMSCAN. However, strong brine acidification and a high concentration of dissolved sulphate were generated in experiments owing to minimal mineral buffering. Also, the movement of kaolin has the potential to block pore throats and reduce permeability. The reaction of the impure CO2-brine with calcite-cemented cap-rock core samples caused the largest porosity changes after reaction through calcite dissolution; to the extent that one sample developed a connection of open pores that extended into the core sub-plug. This has the potential to both favor injectivity but also affect CO2 migration. The dissolution of calcite caused the buffering of acidity resulting in no significant observable silicate dissolution. Clay-rich cap-rock core samples with minor amounts of carbonate minerals had only small changes after reaction. Created porosity appeared mainly disconnected. Changes were instead associated with decreases in density from Fe-leaching of chlorite or dissolution of minor amounts of carbonates and plagioclase. The interbedded sandstone and shale core also developed increased porosity parallel to bedding through dissolution of carbonates and reactive silicates in the sandy layers. Tight interbedded cap-rocks could be expected to act as baffles to fluids preventing vertical fluid migration. Concentrations of dissolved elements including Ca, Fe, Mn, and Ni increased during reactions of several core samples, with Mn, Mg, Co, and Zn correlated with Ca from cap-rock cores. Precipitation of gypsum, Fe-oxides and clays on seal core samples sequestered dissolved elements including Fe through co-precipitation or adsorption. A conceptual model of impure CO2-water-rock interactions for a siliciclastic reservoir is discussed.

Rigel

Image processing algorithms implemented using custom hardware or FPGAs of can be orders-of-magnitude more energy efficient and performant than software. Unfortunately, converting an algorithm by hand to a hardware description language suitable for compilation on these platforms is frequently too time consuming to be practical. Recent work on hardware synthesis of high-level image processing languages demonstrated that a single-rate pipeline of stencil kernels can be synthesized into hardware with provably minimal buffering. Unfortunately, few advanced image processing or vision algorithms fit into this highly-restricted programming model. In this paper, we present Rigel, which takes pipelines specified in our new multi-rate architecture and lowers them to FPGA implementations. Our flexible multi-rate architecture supports pyramid image processing, sparse computations, and space-time implementation tradeoffs. We demonstrate depth from stereo, Lucas-Kanade, the SIFT descriptor, and a Gaussian pyramid running on two FPGA boards. Our system can synthesize hardware for FPGAs with up to 436 Megapixels/second throughput, and up to 297x faster runtime than a tablet-class ARM CPU.

World Gastroenterology Organisation Global Guidelines: GERD Global Perspective on Gastroesophageal Reflux Disease.

PROBIOTICS—THE CONCEPTHistory and DefinitionsA century ago, Elie Metchnikoff (a Russian scientist, Nobel laureate, and professor at the Pasteur Institute in Paris) postulated that lactic acid bacteria (LAB) offered health benefits capable of promoting longevity. He suggested that “intestinal autoint

A case for hierarchical rings with deflection routing: An energy-efficient on-chip communication substrate

This paper is the first to introduce a scalable and energy-efficient hierarchical ring design that relies on deflection routing and guarantees deadlock- and livelock-free packet delivery.We identify key drawbacks of previous hierarchical ring network designs with respect to scalability, performance and energy efficiency.We propose a new hierarchical ring network design that has simple routers with minimal buffering using deflection routing.We provide a new mechanism for guaranteed delivery of traffic in this network.Compared to 5 other alternative designs, we show that our hierarchical ring network design with deflection routing provides both higher energy-efficiency and higher system performance across a wide variety of workloads. Hierarchical ring networks, which hierarchically connect multiple levels of rings, have been proposed in the past to improve the scalability of ring interconnects, but past hierarchical ring designs sacrifice some of the key benefits of rings by reintroducing more complex in-ring buffering and buffered flow control. Our goal in this paper is to design a new hierarchical ring interconnect that can maintain most of the simplicity of traditional ring designs (i.e., no in-ring buffering or buffered flow control) while achieving high scalability as more complex buffered hierarchical ring designs.To this end, we revisit the concept of a hierarchical-ring network-on-chip. Our design, called HiRD (Hierarchical Rings with Deflection), includes critical features that enable us to mostly maintain the simplicity of traditional simple ring topologies while providing higher energy efficiency and scalability. First, HiRD does not have any buffering or buffered flow control within individual rings, and requires only a small amount of buffering between the ring hierarchy levels. When inter-ring buffers are full, our d7sesign simply deflects flits so that they circle the ring and try again, which eliminates the need for in-ring buffering. Second, we introduce two simple mechanisms that together provide an end-to-end delivery guarantee within the entire network (despite any deflections that occur) without impacting the critical path or latency of the vast majority of network traffic.Our experimental evaluations on a wide variety of multiprogrammed and multithreaded workloads and synthetic traffic patterns show that HiRD attains equal or better performance at better energy efficiency than multiple versions of both a previous hierarchical ring design and a traditional single ring design. We also extensively analyze our design's characteristics and injection and delivery guarantees. We conclude that HiRD can be a compelling design point that allows higher energy efficiency and scalability while retaining the simplicity and appeal of conventional ring-based designs.

An Ultra-Low-Latency Guaranteed-Rate Internet for Cloud Services

An Enhanced-Internet network that provides ultra-low-latency guaranteed-rate (GR) communications for Cloud Services is proposed. The network supports two traffic classes, the Smooth and Best-Effort classes. Smooth traffic flows receive low-jitter GR service over virtual-circuit-switched (VCS) connections with negligible buffering and queueing delays, up to 100% link utilizations, deterministic end-to-end quality-of-service (QoS) guarantees, and improved energy efficiency. End-to-end delays are effectively reduced to the fiber time of flight. A new router scheduling problem called the Bounded Normalized-Jitter integer-programming problem is formulated. A fast polynomial-time approximate solution is presented, allowing TDM-based router schedules to be computed in microseconds. We establish that all admissible traffic demands in any packet-switched network can be simultaneously satisfied with GR-VCS connections, with minimal buffering. Each router can use two periodic TDM-based schedules to support GR-VCS connections, which are updated automatically when the router's traffic rate matrix changes. The design of a Silicon-Photonics all-optical packet switch with minimal buffering is presented. The Enhanced-Internet can: 1) reduce router buffer requirements by factors of ≥ 1000; 2) increase the Internet's aggregate capacity; 3) lower the Internet's capital and operating costs; and 4) lower greenhouse gas emissions through improved energy efficiency.

Basic methods for monitoring intracellular Ca2+ in cardiac myocytes using Fluo-3.

In cardiac myocytes, the physiological increase of intracellular calcium, the [Ca(2+)]i transient, elicited during excitation-contraction coupling typically reaches a peak amplitude of up to 1 µm, from a resting value of ∼100 nm, within 50-100 msec, depending on the species. Various conditions will affect the amplitude and rise time of the [Ca(2+)]i transient and, depending on the nature of the Ca(2+) signals under study, a variety of different probes are available for monitoring changes in intracellular Ca(2+). In this protocol, we focus on Fluo-3, which exists in the cytosol in its salt form K5Fluo-3. This form is practically nonfluorescent in the absence of Ca(2+), but the fluorescence increases dramatically on Ca(2+) binding. Although Fluo-3 is a single excitation-emission dye, it has a number of advantages for investigators, including an ideal dissociation constant (Kd) value and high quantum yield, meaning that it can be used at low concentrations that introduce minimal buffering. Here, we describe the basic setup and methodology for recording the global cytosolic [Ca(2+)]i transient with this probe during simultaneous patch-clamp and whole-cell recording of membrane voltage or of ionic currents under voltage clamp.

Visual detection of isothermal nucleic acid amplification using pH-sensitive dyes.

Nucleic acid amplification is the basis for many molecular diagnostic assays. In these cases, the amplification product must be detected and analyzed, typically requiring extended workflow time, sophisticated equipment, or both. Here we present a novel method of amplification detection that harnesses the pH change resulting from amplification reactions performed with minimal buffering capacity. In loop-mediated isothermal amplification (LAMP) reactions, we achieved rapid (<30 min) and sensitive (<10 copies) visual detection using pH-sensitive dyes. Additionally, the detection can be performed in real time, enabling high-throughput or quantitative applications. We also demonstrate this visual detection for another isothermal amplification method (strand-displacement amplification), PCR, and reverse transcription LAMP (RT-LAMP) detection of RNA. The colorimetric detection of amplification presented here represents a generally applicable approach for visual detection of nucleic acid amplification, enabling molecular diagnostic tests to be analyzed immediately without the need for specialized and expensive instrumentation.

The Potential for Dams to Impact Lowland Meandering River Floodplain Geomorphology

The majority of the world's floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We review studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, and interactions with floodplain vegetation. The results are synthesized into a conceptual model of the effects of dams on the major geomorphic influences on floodplain development. This model is used to assess the likely consequences of eight dam and flow regulation scenarios for floodplain geomorphology. Sediment starvation downstream of dams has perhaps the greatest potential to impact on floodplain development. Such effects will persist further downstream where tributary sediment inputs are relatively low and there is minimal buffering by alluvial sediment stores. We can identify several ways in which floodplains might potentially be affected by dams, with varying degrees of confidence, including a distinction between passive impacts (floodplain disconnection) and active impacts (changes in geomorphological processes and functioning). These active processes are likely to have more serious implications for floodplain function and emphasize both the need for future research and the need for an “environmental sediment regime” to operate alongside environmental flows.

Strategic use of feed ingredients and feed additives to stimulate gut health and development in young pigs

There is a wide interest in developing management and feeding strategies to stimulate gut development and health in newly-weaned pigs, in order to improve growth performance while minimizing the use of antibiotics and rather expensive feed ingredients, such as milk products. A better understanding of the mechanisms whereby antibiotics influence animal physiology, as well as appropriate use of disease models and in vitro techniques, will lead to the development of alternatives to in-feed antibiotic. Given the considerable advances made in the understanding of intestinal nutrient utilization and metabolism, a complimentary goal in nutrition might be to formulate young pig diets with the specific task of optimizing the growth, function and health of the gut. Important aspects of gut health-promoting pig diets are: reduced content of protein that is fermented in the pigs' gut, minimal buffering capacity, minimal content of anti-nutritional factors, and supply of beneficial compounds such as immunoglobulins. The optimum dietary level and type of fibre will vary with the nature of enteric disease challenges and production objectives. These diet characteristics are influenced by feed ingredient composition and feed processing, including feed fermentation and application of enzymes. A large number of feed additives have been evaluated that are aimed at (1) enhancing the pig's immune response (e.g. immunoglobulin; ω-3 fatty acids, yeast derived ß-glucans), (2) reducing pathogen load in the pig's gut (e.g. organic and inorganic acids, high levels of zinc oxide, essential oils, herbs and spices, some types of prebiotics, bacteriophages, and anti-microbial peptides), (3) stimulate establishment of beneficial gut microbes (probiotics and some types of prebiotics), and (4) stimulate digestive function (e.g. butyric acid, gluconic acid, lactic acid, glutamine, threonine, cysteine, and nucleotides). When manipulating gut microbiota the positive effects of gut health-promoting microbes should be weighed against the increased energy and nutrient costs to support these microbes. In some instances feed additives have been proven effective in vitro but not effective in vivo. The latter applies in particular to essential oils that have strong anti-microbial activity but appear not to be effective in controlling bacterial pathogens when fed to pigs. A combination of different approaches may provide the most effective alternative to in-feed antibiotics.

Reliable Multicast Transport Protocol: RMTP

This paper presents the design, implementation, and performance of a reliable multicast transport protocol (RMTP). RMTP is based on a hierarchical structure in which receivers are grouped into local regions or domains and in each domain there is a special receiver called a designated receiver (DR) which is responsible for sending acknowledgments periodically to the sender, for processing acknowledgment from receivers in its domain, and for retransmitting lost packets to the corresponding receivers. Since lost packets are recovered by local retransmissions as opposed to retransmissions from the original sender, end-to-end latency is significantly reduced, and the overall throughput is improved as well. Also, since only the DR’s send their acknowledgments to the sender, instead of all receivers sending their acknowledgments to the sender, a single acknowledgment is generated per local region, and this prevents acknowledgment implosion. Receivers in RMTP send their acknowledgments to the DR’s periodically, thereby simplifying error recovery. In addition, lost packets are recovered by selective repeat retransmissions, leading to improved throughput at the cost of minimal additional buffering at the receivers. This paper also describes the implementation of RMTP and its performance on the Internet.

Nutrient fluxes in a snow-dominated, semi-arid forest : Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO3−, NH4+, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl− and SO42− concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.

Organic Solutes and the Recovery of a Bog Stream from Chronic Acidification

Natural organic acids are important in the acid-base chemistry of many natural waters. However, field studies suggest that the degree of acid neutralization provided by natural organic acids is small, even in organic-rich waters. We added sulfuric acid and sodium bicarbonate separately to a bog stream in the Czech Republic to evaluate the role of organic acids in the acidification and subsequent recovery of brown waters subjected to chronically high acid deposition. Despite naturally high organic acid concentrations (dissolved organic carbon [DOC] concentration, 48.9 mg L -1 ; total carboxyl group concentration [C T ], 344 μequiv L -1 ; organic acid anion concentration [RCOO-], 176 μequiv L -1 ), only 10% of the added acid and base were neutralized by the protonation or deprotonation of carboxylic functional groups. Approximately 80% of the acid and base additions remained unbuffered. Release of aluminum and basic cations to solution accounted for the remainder of the added acid and base. A Gaussian model of organic acid dissociation, fitted to our experimental results, explained the variations in RCOO- and the minimal buffering offered by organic solutes. Sulfate and hydrogen ion (H + ) concentrations at the study site declined sharply (ca. 50%) in 1992-1996, but DOC, C T , and RCOO- were unchanged. Our experimental and monitoring results suggest that organic acids are not likely to hinder significantly the recovery of brown water streams in the region from chronic anthropogenic acidification).