Half-hour Period Research Articles

Characteristics of the succinate transport into Saccharomices cerevisiae cellsafter prolonged cold preincubation

A nonconventional approach to the measurement of succinate transport through plasmalemma is proposed. It is based on the conditions in which the succinate oxidation rate is limited by transport through plasmalemma. Impermeable specific inhibitor of plasmalemma dicarboxylate transporter was employed as a tool to optimize conditions for the transport activity assay. For this purpose yeast culture was grown in synthetic medium under selected conditions. After aerobic preincubation of S. cerevisiae cells at 0 degree C (instead of incubation at 15 degrees C), the rate of endogenous respiration decreased substantially and was stabilized during measurements at a level that was five times lower than oxidation rates in the presence of exogenous substrate. This approach allowed for the reproducible determination of K(M) for the dicarboxylate transporter (7.3 +/- 2.1 mM) within a half-hour period. The advantages and drawbacks of this fast, but indirect, assay of slow substrates transport into the cell are compared with conventional methods.

Particulate air pollution as a risk factor for ST-segment depression in patients with coronary artery disease.

The association of particulate matter (PM) with cardiovascular morbidity and mortality is well documented. PM-induced ischemia is considered a potential mechanism linking PM to adverse cardiovascular outcomes. In a repeated-measures study including 5979 observations on 48 patients 43 to 75 years of age, we investigated associations of ambient pollution with ST-segment level changes averaged over half-hour periods measured in the modified V(5) position by 24-hour Holter ECG monitoring. Each patient was observed up to 4 times within 1 year after a percutaneous intervention for myocardial infarction, acute coronary syndrome without infarction, or stable coronary artery disease without acute coronary syndrome. Elevation in fine particles (PM(2.5)) and black carbon levels predicted depression of half-hour-averaged ST-segment levels. An interquartile increase in the previous 24-hour mean black carbon level was associated with a 1.50-fold increased risk of ST-segment depression > or =0.1 mm (95% CI, 1.19 to 1.89) and a -0.031-mm (95% CI, -0.042 to -0.019) decrease in half-hour-averaged ST-segment level (continuous outcome). Effects were greatest within the first month after hospitalization and for patients with myocardial infarction during hospitalization or with diabetes. ST-segment depression is associated with increased exposure to PM(2.5) and black carbon in cardiac patients. The risk of pollution-associated ST-segment depression may be greatest in those with myocardial injury in the first month after the cardiac event.

Observed and Perceived Inconsistencies in U.S. Border Inspections

Observations of traffic inspections at a U.S. land border port of entry in El Paso, TX indicate that the process is highly variable. In a series of 24 half-hour observation periods of ordinary non-commercial traffic, the average inspection duration ranged from 16.6 s to 56.6 s. The proportion of inspections which involved some physical search of the vehicle, as indicated by the inspector leaving the inspection booth, varied from 5% to 56% in different observation periods. In 4 out of 10 cases, the log-mean of inspection duration in simultaneous observations of parallel lanes of traffic differed significantly (p<0.05). This suggests that differences in inspector behavior are responsible for much of the variability of the inspection process. Similar results are found for the SENTRI program. A survey of public perception reveals that a majority of English-language respondents perceive the inspectors to be fair while a majority of Spanish-language respondents perceive the process to be more arbitrary indicating that fairness “depends on the inspector”. Spanish-language respondents are also more likely to report having to submit to additional searches than English-language respondents. A common theme that emerges from the analysis of these two datasets is that efforts to standardize some aspects of inspections, while preserving inspector autonomy, may improve the performance of the process by eliminating variability which organized criminal groups may be able to exploit.

Workforce Design with Movement Restrictions Between Workstation Groups

This paper is concerned with the problem of determining the optimal size and composition of a permanent workforce needed to run a facility when demand is specified by a workstation group (WSG) for up to 24 hours a day, 7 days a week. For full-time employees, a solution is characterized by a bid job, which consists of a five-day-a-week schedule, a lunch break for all shifts, and a set of WSG task assignments for each of the half-hour periods in a shift. In contrast, each part-time employee may be given anywhere from one to six shifts during the week, and each shift may vary from four to eight hours in length. To facilitate supervision, all employees must be assigned to a home WSG, but when idle time exists in their schedules, they can be redeployed to other WSGs for a portion of the day. One of the complicating and unique factors addressed in this paper is the existence of nonsymmetric movement restrictions between WSGs. For example, an employee whose home base is A may be permitted to perform tasks at B, but not vice versa. Because the full problem could not be reduced to a single model, a multistage solution approach was developed. In the first stage, an extended shift-scheduling problem is solved to determine the optimal number of employees and their shifts. The results are postprocessed in subsequent stages to obtain lunch breaks, days off, and task assignments under WSG movement restrictions. In the implementation of the multistage approach, two alternatives were explored. The first was based on the idea of partitioning the WSGs into manageable clusters and then solving them in series. The second involved the direct solution of an integer programming formulation of the task assignment problem with home-base restrictions and WSG movement restrictions, but for a fixed workforce. An iterative scheme was used to adjust the size of the workforce until all constraints were satisfied and overall optimality was achieved. Testing was done with data provided by the U.S. Postal Service (USPS) mail processing and distribution center (P&amp;DC) in Dallas. The computations showed that the second alternative always yielded the smaller workforce and was always able to find good solutions within 30 minutes.

Intraday pattern in liquidity covariation: evidence from NYSE listed firms

Microstructure literature suggests common factors in liquidity measures. However, research on the intraday behaviour of liquidity commonality is scant. Because of higher information and inventory holding costs during the first and last half-hours of trading, we argue that liquidity covariations should increase during these half-hour trading periods. Our results from NYSE intraday data support a U-shaped pattern for liquidity covariation. These results have important implications for regulators, investors and academics.

High-power, blue-light generation in a dual-structure, periodically poled, stoichiometric LiTaO3 crystal

High-power blue light was generated from a diode-side-pumped Q-switched 1319 nm Nd:YAG laser with a periodically poled, stoichiometric LiTaO3 (PPSLT) crystal. The PPSLT sample used in this experiment consists of two segments in series: the first segment has a period of 14.08 μm for the second harmonic generation (SHG) and the second segment has periods of around 4.6 μm for the generation of blue light by mixing fundamental and SH. An average power of 466 mW of a 440 nm blue light was obtained at the fundamental power of ∼5.4 W with a conversion efficiency of 8.6%. The output power fluctuated by 3% over a half-hour period. This result indicates that our scheme is a practical method to construct a reliable compact blue laser.

Thermal Stability of Ti/Mo Schottky Contacts on p-Si and Defects Introduced in p-Si during Electron Beam Deposition of Ti/Mo

In this study we have investigated the thermal stability (in the range 100 oC - 900 oC) of defects introduced in p-Si by electron beam deposition (EBD) of Ti and Ti/Mo Schottky contacts. The depletion regions below these contacts were probed by conventional deep level transient spectroscopy (DLTS) as well as Laplace (high-resolution) DLTS (L-DLTS). We have chosen Ti as the Schottky contact because the barrier height of Ti/p-Si (0.53 eV) is close to that of TiSi2/p-Si (0.50 eV) that forms after annealing at 600 – 650 oC. The Mo was added on top of the Ti in order to prevent annealing degradation. These contacts were annealed in Ar at temperatures of up to 900 oC in 100 oC steps for half-hour periods. Current – voltage (I-V) and capacitance – voltage (C-V) measurements were used to monitor the quality of the Schottky contacts. DLTS was performed after each annealing cycle to monitor the presence of the EBD-induced defects and to obtain heir electronic properties. We have found that that the Ti/Mo contacts were superior to the Ti contacts. Their (Ti/Mo) barrier height after EBD was 0.52 eV and it gradually increased to 0.56 eV after annealing at 500 oC - 600oC and then dropped to 0.50 eV annealing at 700 oC. DLTS revealed that the main defects introduced during metallization are hole traps H(0.17), H(0.23), H(0.37) and H(0.49). Annealing at 350 oC introduced an additional hole trap H(0.39). After annealing at 550 oC all defects were removed from the depletion region.

Nash equilibria in electricity markets with discrete prices

In this paper we analyse the equilibrium structure for a particular type of electricity market. We consider a market with two generators offering electricity into a pool. Generators are centrally dispatched, with cheapest offers used first. The pool price is determined as the highest-priced offer dispatched, and both generators are paid this price for all the electricity they provide. First generators set their price points (at which bids will later be made) and these are announced. Then each generator chooses the quantities to offer at each price. This reflects the behaviour of the Australian electricity market in which prices are set for 24-hours at a time, but different quantities can be offered within each half-hour period. The demand for electricity is uncertain when offers are made (and is drawn from a probability distribution known to both players). We begin by analysing an example of this two stage game for a simple case where only one price can be chosen. The main results of the paper concern the structure of a Nash equilibrium for the quantity-setting sub-game in which each player aims to maximise their expected profit when prices have already been announced. The distribution of demand plays an important role in the existence of a Nash equilibrium. In the quantity setting game there may be Nash equilibria which are not stable. We show that, under certain circumstances, if the equilibrium offers are sufficiently close to the generators’ marginal costs, then the equilibrium will be stable.

The influence of diazepam on atropine reversal of behavioural impairment in dichlorvos-treated rats.

Acute effects on the behaviour of the organophosphate insecticide dichlorvos and its standard antidotes possessing behavioural activity, atropine and diazepam, were studied separately and in combinations in male Wistar rats. In the spontaneous locomotor activity test, dichlorvos and diazepam decreased, whereas atropine increased performance. The effect of dichlorvos was obtained at a dose (5 mg/kg) that induced overt intoxication, and could not be reversed during first half hour-period after administration of any combination of drugs. In the other two tests, active avoidance learning and rotarod performance, the effective dose of dichlorvos (2 mg/kg) was devoid of somatic signs of intoxication. In these more sensitive tests, the effective atropine dose (40 mg/kg) completely reversed dichlorvos-induced incapacitation. In the rotarod test, diazepam (0.5 mg/kg) contributed to the incapacitating effect of dichlorvos, and impeded desirable influence of atropine as well. In the active avoidance test, diazepam (2.5 mg/kg) contributed to failure to escape; it did not influence the dichlorvos-induced decrease of avoidance performance, nor did it impair the completely reversing effects of atropine. The results point to the possible summation of acute incapacitating effects of organophosphates and diazepam on motor performance, which seems to be, at least partly, antagonized by sufficiently high doses of atropine. However, taking into account the long-term neuroprotective role of the anticonvulsant diazepam, and hence its delayed beneficial influences on behaviour, the immediate testing of atropine/diazepam treatment of organophosphate intoxication in active avoidance paradigm could possess beside sensitivity the predictive value as well.

A Class of Models for Aggregated Traffic Volume Time Series

Summary The development of time series models for traffic volume data constitutes an important step in constructing automated tools for the management of computing infrastructure resources. We analyse two traffic volume time series: one is the volume of hard disc activity, aggregated into half-hour periods, measured on a workstation, and the other is the volume of Internet requests made to a workstation. Both of these time series exhibit features that are typical of network traffic data, namely strong seasonal components and highly non-Gaussian distributions. For these time series, a particular class of non-linear state space models is proposed, and practical techniques for model fitting and forecasting are demonstrated.

Encouraging stair use: stair-riser banners are better than posters.

Increasing physical activity levels among a largely sedentary public is a health priority.1 Lifestyle exercise, such as walking or stair climbing, has been recommended because it provides substantial health benefits and fits easily into daily routines.2 Opportunities for stair climbing in workplaces, public buildings, and the home are frequently available to most population groups. Studies conducted in both the United States and the United Kingdom have shown that posters at the “point of choice” between escalators and stairs can increase stair use.3–6 As a result, physical activity promoters have championed the use of such posters. In a recent study, however, messages placed as banners on alternate stair risers were associated with a greater increase in shoppers' stair use than that typically observed with posters.7 To confirm the superiority of these banners in promoting stair climbing, we systematically compared the use of poster prompts and stair-riser banners. The study was conducted at 2 shopping malls; both sites had 28-step staircases with adjacent escalators. Following a coding system,3 an observer recorded the number of people using the escalators and stairs on alternate days at each location. Observations were made between 11 am and 1 pm to include day and lunchtime shoppers. At the control site, a 2-week baseline period was followed by 4 weeks during which a poster that read “Stay healthy, use the stairs” was displayed. Use of this poster had been found to be effective in previous research.3 At the experimental site, 2 weeks of baseline observation and 2 weeks of the poster intervention were followed by 2 weeks during which banners, containing mulitple messages, were placed on the stair risers, as in our earlier study.7 Logistic regression analyses were conducted with escalator–stair use as the dichotomous outcome variable. Overall pedestrian traffic volume, a potential confounding variable,3 was calculated as the total number of people using the escalators and stairs during each half-hour period. Traffic volume was entered into the logistic regression models as a continuous variable. Sex, age, and ethnicity were also added to the models, in that previous research had demonstrated their importance.3–6 Figure 1 ▶ illustrates the effects of the poster and banner conditions in the 2 shopping malls. At the control site (n = 12 018), the rate of stair use increased from 2.2% at baseline to 4.8% during the first 2 weeks of the poster exposure but fell slightly to 4.1% during the second 2 weeks. At the experimental site (n = 11 961), stair use increased from 2.4% at baseline to 4.0% when the poster was in place and rose to 6.7% when the banners were displayed on the stair risers. FIGURE 1— Stair use at baseline in poster and banner conditions in the control and experimental shopping malls. Logistic regression analyses revealed that stair use increased at both sites during the first 2 weeks in which the poster was displayed (odds ratio [OR] = 2.18, 95% confidence interval [CI] = 1.69, 2.80), with no significant differences between the sites. During the second intervention period, there was an interaction between the sites (OR = 2.06, 95% CI = 1.48, 2.87) such that rates of stair use were higher with the banners at the experimental site than with the poster at the control site. There are several reasons why the banners were more effective than the poster in encouraging stair use. First, the banners were highly visible. In our earlier studies, 76% of interviewees reported seeing these banners,7 whereas only a third reported noticing the poster used.8 Second, while the poster included only one health-related message, the banners contained multiple messages, such as “Keep fit,” “Be active,” and “Free exercise.” As such, they are likely to appeal to a broader population range.9 Regular stair climbing has been associated with discernible health gains.10 Accordingly, if large population groups are regularly exposed to motivating stair banners instead of the posters currently used by health promoters, the public health dividends could be considerable.

A Temperature-Based Model for Latent-Period Duration in Stem Rust of Perennial Ryegrass and Tall Fescue

ABSTRACT A temperature-response curve for latent-period duration in stem rust (caused by Puccinia graminis subsp. graminicola) on perennial ryegrass and tall fescue was developed from constant-temperature experiments with inoculated plants and evaluated in field experiments. Under constant-temperature conditions, time from infection to 50% of pustules erupted for perennial ryegrass ranged from 54 days at 3.5 degrees C to 5.9 days at 26.5 degrees C. The latent period (LP(50)) duration of tall fescue was 69 and 8.5 days at these respective temperatures. The dependence of latent-period completion rate on temperature was best described as a linear increase in rate with temperature up to approximately 26 degrees C, then an exponential decline with temperature up to the maximum (lethal) temperature of approximately 35.5 degrees C. LP(20), the time required for 20% of open pustules to appear, was used as an estimator of latent-period duration for field observations. Percentage of one latent period completed per half hour (half-hourly rate), for perennial ryegrass was modeled as (0.0156T - 0.0206) {1 - exp[0.497(T - 35.5)]}, where T = average temperature ( degrees C) during the half-hour period. For tall fescue the modeled rate was (0.0109T - 0.00214) {1 - exp[0.417(T - 35.5)]}. Latent periods modeled by these equations were compared with observed latent periods in field experiments with potted plants, where half-hourly temperatures were measured. Linear regressions of modeled versus observed latent periods had adjusted r(2) values of 0.96 for perennial ryegrass and 0.93 for tall fescue. The latent-period equations could be used as components of a weather-based disease advisory model to optimize fungicide use in stem-rust management on these crops.

Spatial and temporal variation in gas exchange over the lower surface of Phaseolus vulgaris L. primary leaves

This paper describes spatio-temporal variation in gas exchange over the lower surface of primary leaves of glasshouse-grown Phaseolus vulgaris L. plants. Simultaneous measurements of assimilation and water vapour conductance were made with a small area cuvette attached to an infra-red gas analyser. The plants were kept in glass chambers so that the external gaseous environment could be controlled. Observations are reported from four half-hour periods during a day in which the ambient PPFD, while variable, was close to saturating for photosynthesis. 'Snapshot' measurements of gas exchange were made at 20 positions on the leaf surface using a stratified random out-to-in strategy, which avoided disturbance of yet-to-be-measured sites. Data were mapped using the 'Unimap' cartographic program. For any given measurement period, gas exchange varied greatly over the leaf surface : typically, net assimilation (A) varied by over 4-fold and leaf conductance (g I ) by over 3-fold. Estimated intracellular pressures of CO 2 and leaf temperatures showed less relative variation both in space and time. Comparing measurement periods, the spatial patterns of variation in A and g, were dissimilar. Moreover, at different sites on the leaf, the trends in a given variable could be in opposite directions, while external conditions were relatively constant. Although the correlation between A and g, was significant overall, there was a large degree of scatter in the data and zones of high g, often corresponded to areas of low A. Depending on the basis of calculation, A was as much as 63% lower than a value predicted on the basis of steady-state measurements for the appropriate mean irradiance. It was not possible to deduce from the relationships between pairs of variables which factors were most important in determining A and g I at any given time or space, but g I did not appear to be the only factor limiting A. It is hypothesized that the observed variation in gas exchange, the lack of close correspondence between g 1 and A and the reduction in photosynthesis compared with the apparent potential value are all phenomena that arise from differences in the induction times for these variables following changes in conditions, interacting with other factors associated with position on the leaf.

Impact of interruptions and distractions on dispensing errors in an ambulatory care pharmacy.

A possible association between interruptions and distractions and the occurrence of dispensing errors was investigated. Fourteen pharmacists and 10 technicians in an ambulatory care pharmacy at a general medical-surgical hospital were tested for distractibility by using the group embedded figures test (GEFT) as well as for visual acuity and hearing. They were videotaped as they filled prescriptions during a 23-day period in 1992. A study investigator compared each filled prescription with the physician's written order, noted details of deviations, verified with the pharmacist any errors that occurred, and asked the pharmacist to correct the error if necessary. Interruptions and distractions were detected and characterized by reviewing the videotapes. None of the study participants had significant hearing or visual impairment. There was a significant association between GEFT scores and error rates. A total of 5072 prescriptions were analyzed, and 164 errors were detected, for an overall error rate of 3.23%. Wrong label information was the most common type of error (80% of errors detected). A total of 2022 interruptions (mean +/- S.D. per half hour per subject, 2.99 +/- 2.70) and 2457 distractions (mean +/- S.D. per half hour per subject, 3.80 +/-3.17) were detected. The error rate for sets of prescriptions with one or more interruptions was 6.65% and for sets during which there were one or more distractions, 6.55%. Interruptions and distractions per half hour were both significantly associated with errors. In an ambulatory care pharmacy, interruptions and distractions over a half-hour period were associated with dispensing errors, a majority of which involved incorrect label information.

Measuring Sensible Heat Flux Density over Pasture Using the ct2-Profile Method

Two large-aperture infrared scintillometers were positioned at heights (z) of 10 and 1.5 m with beams propagated horizontally over pasture for distances of 3.1 km and 141 m, respectively. From each scintillometer a half-hourly average value of the path-averaged, temperature-structure parameter (CT2) was obtained in unstable atmospheric conditions. The result suggested CT2 to scale with height as z-2/3. Using the CT2-profile method a path-averaged measure of the Obukhov length (L0) was calculated for each half-hour period, whence L0 was used to determine the friction velocity, u* and the surface-layer temperature scaling parameter, T*. The scintillometer-based sensible heat flux density Hsc was then calculated from Hsc = ρ Cpu*T*. A time series of half-hourly averaged Hsc compared to Hec obtained by the eddy covariance method agreed to within 10%, with R2 = 0.67, for a range of unstable conditions (- 0.2 ≤ z/L0 ≤ - 0.01).

Large-Eddy Simulation of Contrails

Numerical simulations of contrails have been performed to investigate the role of various external parameters and physical processes in the life cycle of contrails. The general idea underlying the model is that of a large-eddy model. The model explicitly represents the large-scale three-dimensional motions (10-m grid resolution), while small-scale turbulence is parameterized; it contains a detailed microphysical model and it takes into account infrared radiative cooling in cloudy conditions and the vertical shear of the ambient flow. The model is applied to conditions typical for those under which contrails could be observed, that is, in an atmosphere which is supersaturated with respect to ice and at a temperature of 220 K. The simulations begin in the late dispersion phase (i.e., about 103 s after exhaust) and trace the evolution of the contrails for a half-hour period. Coherent structures can be identified within these clouds with vertical velocity fluctuations of the order of 0.1 m s−1 that are generated mainly by buoyancy due to latent heat release. In addition, the sensitivity runs undertaken as a test of the model to a change in significant physical processes or external parameters indicate that the contrail evolution is controled primarily by humidity, temperature, and static stability of the ambient air and secondarily by the baroclinicity of the atmosphere. Moreover, it turns out that the initial ice particle concentration and radiative processes are of minor importance in the evolution of contrails, at least during the 30-min simulation period.

Evaporation from an eastern Siberian larch forest

Total forest evaporation ( λE), understorey evaporation, and environmental variables were measured on nine summer days under different weather conditions in a 130-year-old stand of Larix gmelinii (Rupr.) Rupr. trees located 160 km south of Yakutsk in eastern Siberia, Russia (61°N, 128°E, 300m above sea-level (a.s.l.)). Tree and broad-leaved understorey vegetation one-sided leaf area indices were 1.5 and 1.0, respectively. Agreement of λE and sensible heat flux ( H), both measured by eddy covariance, and the available energy ( R a) was generally good: ( H + λE) = 0.83 R a + 9 W m −2 with r 2 = 0.92 for 364 half-hour periods and the mean ± 95% confidence limit was 129 ± 17 for ( H + λE) and 144 ± 19 for R a. Daily E was 1.6–2.2 min, less than half of the potential evaporation rate and accounting for 31–50% of R a, with the lowest percentage on clear days. A perusal of the sparse literature revealed that average daily E of boreal coniferous forest during the tree growing season (1.9 mm day −1 for this study) is relatively conservative, suggesting that low evaporation rates are a feature of this biome's energy balance. Using the Penman-Monteith equation, the maximum bulk-surface conductance ( G smax) was 10 mm s −1. E and G s were regulated by irradiance, air saturation deficit, and surface soil water content during a week-long dry period following 20 mm rainfall. From lysimeter measurements, 50% of E emanated from the understorey at a rate proportional to R a. Based on the measurements and published climatological data, including average annual precipitation equal to 213 mm, water balance calculations indicated growing season forest E equal to 169 mm, the occurrence of a late summer-autumn soil water deficit, and annual runoff of 44 mm by snowmelt.

Organizing a social event—A difficult problem of combinatorial optimization

This interesting problem arose in the context of organizing a “progressive party” at a yachting rally. Some yachts were to be designated hosts; the crews of the remaining yachts would then visit the hosts for six successive half-hour periods. A guest crew could not revisit the same host, and two guest crews could not meet more than once during the evening. Additional constraints were imposed by the capacities of the host yachts and the crew sizes of the guests. Although this problem has many of the classical features of combinatorial optimization problems, it does not belong to any previously known class of problem. Integer programming formulations which included all the constraints resulted in very large models and all attempts to find a solution failed. However by solving a simple relaxation of the problem using linear programming we obtained a lower bound for the solution, which combined with a feasible solution obtained (spectacularly easily) by constraint programming led to an optimal solution. We describe our computational experience and discuss the features of this problem which account for the failure and success of the two approaches.

The progressive party problem: Integer linear programming and constraint programming compared

Many discrete optimization problems can be formulated as either integer linear programming problems or constraint satisfaction problems. Although ILP methods appear to be more powerful, sometimes constraint programming can solve these problems more quickly. This paper describes a problem in which the difference in performance between the two approaches was particularly marked, since a solution could not be found using ILP. The problem arose in the context of organizing a “progressive party” at a yachting rally. Some yachts were to be designated hosts; the crews of the remaining yachts would then visit the hosts for six successive half-hour periods. A guest crew could not revisit the same host, and two guest crews could not meet more than once. Additional constraints were imposed by the capacities of the host yachts and the crew sizes of the guests. Integer linear programming formulations which included all the constraints resulted in very large models, and despite trying several different strategies, all attempts to find a solution failed. Constraint programming was tried instead and solved the problem very quickly, with a little manual assistance. Reasons for the success of constraint programming in this problem are identified and discussed.

Methane emissions from a landfill measured by eddy correlation using a fast response diode laser sensor

We describe a fast response methane sensor based on the absorption of radiation generated with a near-infrared InGaAsP diode laser. The sensor uses an open path absorption region 0.5 m long; multiple pass optics provide an optical path of 50 m. High frequency wavelength modulation methods give stable signals with detection sensitivity (S/N=1, 1 Hz bandwidth) for methane of 65 ppb at atmospheric pressure and room temperature. Improvements in the optical stability are expected to lower the current detection limit. We used the new sensor to measure, by eddy correlation, the CH4 flux from a clay-capped sanitary landfill. Simultaneously we measured the flux of CO2 and H2O. From seven half-hourly periods of data collected after a rainstorm on November 23, 1991, the average flux of CH4 was 17 mmol m−2 hr−1 (6400 mg CH4 m−2 d−1) with a coefficient of variation of 25%. This measurement may underrepresent the flux by 15% due to roll-off of the sensor response at high frequency. The landfill was also a source of CO2 with an average flux of 8.1 mmol m−2 hr−1 (8550 mg CO2 m−2 d−1) and a coefficient of variation of 26%. A spectral analysis of the data collected from the CH4, CO2, and H2O sensors showed a strong similarity in the turbulent transfer mechanisms.