Scattering Properties of the Ocean Surface: The Miller–Brown–Vegh Model Revisited

We review the model of Miller-Brown-Vegh (MBV) that is commonly used to describe scattering from the ocean surface. The model has been built on two essential elements: the Kirchhoff approximation and an assumption regarding the probability distribution of the ocean surface elevations. A comparison with theoretical results preceeding the MBV model as well as with experimental data suggest that the MBV model is inconsistent with the predicted and observed probability distribution of sea waves. Here, a scattering model based on more rigorous statistics of the ocean surface is considered instead. The analysis we present offers an explanation as well as a remedy for the reported tendency of models describing propagation in evaporation ducts to overestimate the signal's intensity at the receiver.     

Symposium review: Uncertainties in enteric methane inventories,measurement techniques,and prediction models

Ruminant production systems are important contributors to anthropogenic methane (CH₄) emissions, but there are large uncertainties in national and global livestock CH₄ inventories. Sources of uncertainty in enteric CH₄ emissions include animal inventories, feed dry matter intake (DMI), ingredient and chemical composition of the diets, and CH₄ emission factors. There is also significant uncertainty associated with enteric CH₄ measurements. The most widely used techniques are respiration chambers, the sulfur hexafluoride (SF₆) tracer technique, and the automated head-chamber system (GreenFeed; C-Lock Inc., Rapid City, SD). All 3 methods have been successfully used in a large number of experiments with dairy or beef cattle in various environmental conditions, although studies that compare techniques have reported inconsistent results. Although different types of models have been developed to predict enteric CH₄ emissions, relatively simple empirical (statistical) models have been commonly used for inventory purposes because of their broad applicability and ease of use compared with more detailed empirical and process-based mechanistic models. However, extant empirical models used to predict enteric CH₄ emissions suffer from narrow spatial focus, limited observations, and limitations of the statistical technique used. Therefore, prediction models must be developed from robust data sets that can only be generated through collaboration of scientists across the world. To achieve high prediction accuracy, these data sets should encompass a wide range of diets and production systems within regions and globally. Overall, enteric CH₄ prediction models are based on various animal or feed characteristic inputs but are dominated by DMI in one form or another. As a result, accurate prediction of DMI is essential for accurate prediction of livestock CH₄ emissions. Analysis of a large data set of individual dairy cattle data showed that simplified enteric CH₄ prediction models based on DMI alone or DMI and limited feed- or animal-related inputs can predict average CH₄ emission with a similar accuracy to more complex empirical models. These simplified models can be reliably used for emission inventory purposes.     

Short-term methane emissions from 2 dairy farms in California estimated by different measurement techniques and US Environmental Protection Agency inventory methodology: A case study

Reported estimates of CH₄ emissions from ruminants and manure management are up to 2 times higher in atmospheric top-down calculations than in bottom-up (BU) inventories. We explored this discrepancy by estimating CH₄ emissions of 2 dairy facilities in California with US Environmental Protection Agency (US EPA) methodology, which is used for BU inventories, and 3 independent measurement techniques: (1) open-path measurements with inverse dispersion modeling (hereafter open-path), (2) vehicle measurements with tracer flux ratio method, and (3) aircraft measurements with the closed-path method. All 3 techniques were used to estimate whole-facility CH₄ emissions during 3 to 6 d per farm in the summer of 2016. In addition, open-path was used to estimate whole-facility CH₄ emissions over 13 to 14 d per farm in the winter of 2017. Our objectives were to (1) compare whole-facility CH₄ measurements utilizing the different measurement techniques, (2) compare whole-facility CH₄ measurements to US EPA inventory methodology estimates, and (3) compare CH₄ emissions between 2 dairies. Whole-facility CH₄ estimates were similar among measurement techniques. No seasonality was detected for CH₄ emissions from animal housing, but CH₄ emissions from liquid manure storage were 3 to 6 times greater during the summer than during the winter measurement periods. The findings confirm previous studies showing that whole-facility CH₄ emissions need to be measured throughout the year to estimate and evaluate annual inventories. Open-path measurements for liquid manure storage emissions were similar to monthly US EPA estimates during the summer, but not during the winter measurement periods. However, the numerical difference was relatively small considering yearly emission estimates. Manure CH₄ emissions contributed 69 to 79% and 26 to 47% of whole-facility CH₄ emissions during the summer and winter measurement periods, respectively. Methane yields from animal housing were similar between farms (on average 20.9 g of CH₄/kg of dry matter intake), but CH₄ emissions normalized by volatile solids (VS) loading from liquid manure storage (g of CH₄ per day/kg of VS produced by all cattle per day) at 1 dairy were 1.7 and 3.5 times greater than at the other during the summer (234 vs. 137 g of CH₄/kg of VS) and winter measurement periods (78 vs. 22 g of CH₄/kg of VS), respectively. We attributed much of this difference to the proportion of manure stored in liquid (anaerobic) form, and suggest that manure management practices that reduce the amount of manure solids stored in liquid form could significantly reduce dairy CH₄ emissions.     

Peas can replace soybean meal and corn grain in dairy cow diets

The objective of this experiment was to investigate the effect of a partial substitution of soybean meal and corn grain with field peas in dairy cow diets on intake, milk yield and composition, nutrient digestibility, and urinary and fecal N losses. Twenty-four lactating Holstein cows were blocked into 2 groups based on parity, days in milk, and milk yield at the end of a 2-wk covariate period. Cows within group were randomly assigned to 1 of 2 treatments: control and pea diets. Approximately 45% of the corn grain and 78% of the soybean meal in the control diet were replaced with 15% (dry matter basis) field peas in the experimental diet. The peas used in the trial contained 25% crude protein and an estimated 1.98 Mcal of net energy for lactation/kg. The experiment continued for 70 d. Dry matter intake (25.9 and 26.3 kg/d; control and pea diets, respectively), milk yield (35.4 and 35.6 kg/d), 4% fat-corrected milk yield (33.0 and 34.6 kg/d), milk fat (3.54 and 3.76%) and protein (3.00 and 2.99%) content and yields, and milk N efficiency (26 and 24%) were not affected by diet. Concentration of milk urea nitrogen was also not affected by treatment (14.3 and 15.0 mg/dL, respectively). Intake of organic matter and N were not affected by diet, but intake of neutral detergent fiber was lower and that of starch greater with the control diet. Total tract apparent digestibility of starch was lower (92.1 vs. 88.3%, respectively) and that of dry matter and organic matter tended to be lower with the pea compared with the control diet. Urinary and fecal N losses were not different between the 2 diets. Panel evaluation of milk from the 2 diets indicated no differences in the organoleptic characteristics of milk. This experiment demonstrated that field peas could be safely fed to high-producing dairy cows at a 15% inclusion rate, replacing soybean meal and corn grain. At this inclusion rate, no effects on milk yield or milk composition were observed.     

Effects of Saccharomyces cerevisiae-based direct-fed microbial and exogenous enzyme products on enteric methane emission and productivity in lactating dairy cows

The objective of this experiment was to investigate the effects of a Saccharomyces cerevisiae-based direct-fed microbial product (SDM) and an exogenous enzyme product (ENZ) on enteric methane emission, milk yield and composition, total-tract digestibility of nutrients, ruminal fermentation, and nitrogen excretion and secretion in lactating dairy cows. Eighteen Holstein cows were used in a 3 × 3 Latin square design experiment with three 28-d periods. Treatments were (1) control (no additive), (2) 28 g of SDM/d per cow, or (3) 10 g of ENZ/d per cow. Treatments were top-dressed at the time of feeding. The basal diet consisted of (dry matter basis) 60% forage and 40% concentrates and contained 16.5% crude protein and 32.0% neutral detergent fiber. Treatments had no effect on enteric methane production, yield (methane per kg of dry matter intake, DMI), or intensity (methane per kg of energy-corrected milk yield). Carbon dioxide production was similar among treatments. Compared with control, SDM increased milk yield by 2 kg/d without affecting DMI or feed efficiency. Supplementation of the diet with ENZ did not affect DMI, milk yield, or feed efficiency. Concentrations and yields of milk fat, true protein, and lactose, and energy-corrected milk yield were not different among treatments. Neither SDM nor ENZ had an effect on total-tract digestibility of nutrients or nitrogen excretion and secretion. Concentration of total volatile fatty acids (VFA) in ruminal fluid was increased by both SDM and ENZ, and rumen pH was decreased by SDM compared with the control. At levels similar to the control DMI, the increased concentration of VFA in ruminal fluid of cows receiving SDM suggests an increased postruminal supply of energy and may partly explain the increased milk yield with that treatment. However, it is important to note that milk composition and energy-corrected milk yield were not affected by treatment.     

Compound Fresnel Zone Lens Conformal to Truncated Cone: Antenna Application

A millimeter wave antenna consisting of two Fresnel zone plate lenses, plane and conical, is examined numerically by use of the vector diffraction theory. The lenses are of Wood-Wiltse (double-dielectric) or Soret (half-open) type, and are designed for the frequency of 117 GHz. The lenses are made conformal to a truncated circular cone with a base diameter of 500 mm and a plateau diameter of 250 mm. Designs for two opening semi-angles, 45° and 75° each of them with a particular lens thickness are presented. For the angle of 90° the cone lens becomes a plane ring lens, which in combination with the plateau zone lens forms a plane lens of size equal to the cone base diameter. Illuminated by directive feeds set at a focal distance of 525 mm from the cone apex, the double-dielectric and half-open compound and plane lenses, form three pairs of Fresnel zone lens antennas, the co-polar and cross-polar radiation characteristics of which have been compared numerically. The double-dielectric lens antennas examined are about 5 dB superior in gain to the half-open lens antennas, which has a gain of approximately 45 dBi. Because all lenses are of equal transverse aperture, the corresponding lens antennas exhibit the same ?3 dB beamwidth of about 0.33 degrees. The plane zone lens antenna is very thin and simple. Instead, the antenna comprising a 3-D compound Fresnel zone lens is thicker but can be made conformal to a specific surface shape and possesses more levels of design and optimization freedom.     

Influence of Coupling Agents on Melt Flow Behavior of Natural Fiber Composites

The influence of coupling agents on the melt rheological properties of natural fiber composites has been investigated in this work using capillary and rotational rheometers. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the filler wetting and the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides relatively larger increase of the viscosity of the composites. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings. Entrance pressure loss in capillaries is also influenced by polymer matrix and coupling agent used.

     

电容式接近检测技术在汽车电子中的应用

汽车电子应用领域对接近检测传感器的需求一直在稳定攀升,这种传感器无需物理接触,就能够可靠地检测出靠近传感器表面的物体,可应用于:●汽车门禁控制:检测手靠近门把,进而启动开锁程序。●当手掌靠近屏幕表面时,就能照亮和唤醒触摸屏     

Effects of dietary protein concentration and coconut oil supplementation on nitrogen utilization and production in dairy cows

The objective of this study was to investigate the effect of metabolizable protein (MP) deficiency and coconut oil supplementation on N utilization and production in lactating dairy cows. The hypothesis of the study was that a decrease in ruminal protozoal counts with coconut oil would increase microbial protein synthesis in the rumen, thus compensating for potential MP deficiency. The experiment was conducted for 10 wk with 36 cows (13 primiparous and 23 multiparous), including 6 ruminally cannulated cows. The experimental period, 6 wk, was preceded by 2-wk adaptation and 2-wk covariate periods. Cows were blocked by parity, days in milk, milk yield, and rumen cannulation and randomly assigned to one of the following diets: a diet with a positive MP balance (+44 g/d) and 16.7% dietary crude protein (CP) concentration (AMP); a diet deficient in MP (−156 g/d) and 14.8% CP concentration (DMP); or DMP supplemented with approximately 500 g of coconut oil/head per day (DMPCO). Ruminal ammonia tended to be greater and plasma urea N (20.1, 12.8, and 13.1 mg/dL, for AMP, DMP, and DMPCO diets, respectively) and milk urea N (12.5, 8.3, and 9.5 mg/dL, respectively) were greater for AMP compared with DMP and DMPCO. The DMPCO diet decreased total protozoa counts (by 60%) compared with DMP, but had no effect on the methanogens profile in the rumen. Total tract apparent digestibility of dry matter and CP was decreased by DMP compared with AMP. Fiber digestibility was lower for both DMP and DMPCO compared with AMP. Urinary N excretion was decreased (by 37%) by both DMP and DMPCO compared with AMP. The DMP and DMPCO diets resulted in greater milk N efficiency compared with AMP (32.0 and 35.1 vs. 27.6%, respectively). Milk yield was decreased by both DMP and DMPCO compared with AMP (36.2, 34.4, and 39.3 kg/d, respectively) and coconut oil supplementation suppressed feed intake and caused milk fat depression. Coconut oil supplementation decreased short-chain fatty acid (C4:0, C6:0, and C8:0) concentration and increased medium-chain (C12:0 and C14:0) and total trans fatty acids in milk. Overall, the MP-deficient diets decreased N losses, but could not sustain milk production in this study. Coconut oil decreased feed intake and similar to DMP, suppressed fiber digestibility. Despite decreased protozoal counts, coconut oil had no effect on the methanogen population in the rumen.