Search

An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a spectral index of -2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11-year data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red noise process with low-spectral index noise, and use a tailored noise model to remove these effects., 14 pages, 13 figures, fixed typo in abstract of earlier version

The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. 2013 was the first to show a short-term (~100-200 days) reduction in the electron content along the line of sight to PSR J1713+0747 in data from 2008 (approximately MJD 54750) based on an apparent dip in the dispersion measure of the pulsar. We report on a similar event in 2016 (approximately MJD 57510), with average residual pulse-arrival times of approximately 3.0,-1.3, and -0.7 microseconds at 820, 1400, and 2300 MHz, respectively. Timing analyses indicate possible departures from the standard nu^-2 dispersive-delay dependence. We discuss and rule out a wide variety of potential interpretations. We find the likeliest scenario to be lensing of the radio emission by some structure in the interstellar medium, which causes multiple frequency-dependent pulse arrival-time delays., 9 pages, 3 figures, published in ApJ

Observations indicate that nearly all galaxies contain supermassive black holes (SMBHs) at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the recently-released North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95\% upper limits on the strength of GWs from such sources as a function of GW frequency and sky location. We placed a sky-averaged upper limit on the GW strain of $h_0 < 7.3(3) \times 10^{-15}$ at $f_\mathrm{gw}= 8$ nHz. We also developed a technique to determine the significance of a particular signal in each pulsar using ``dropout' parameters as a way of identifying spurious signals in measurements from individual pulsars. We used our upper limits on the GW strain to place lower limits on the distances to individual SMBHBs. At the most-sensitive sky location, we ruled out SMBHBs emitting GWs with $f_\mathrm{gw}= 8$ nHz within 120 Mpc for $\mathcal{M} = 10^9 \, M_\odot$, and within 5.5 Gpc for $\mathcal{M} = 10^{10} \, M_\odot$. We also determined that there are no SMBHBs with $\mathcal{M} > 1.6 \times 10^9 \, M_\odot$ emitting GWs in the Virgo Cluster. Finally, we estimated the number of potentially detectable sources given our current strain upper limits based on galaxies in Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris cosmological simulation project. Only 34 out of 75,000 realizations of the local Universe contained a detectable source, from which we concluded it was unsurprising that we did not detect any individual sources given our current sensitivity to GWs., 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send any comments/questions to S. J. Vigeland (vigeland@uwm.edu)

A number of studies have reported performance by spring-calving cows grazing Neotyphodium -infected fescue [E+, Lolium arundinaceum (Schreb.) Darbysh.], but post-weaning calf performance from the majority of those studies is limited. Furthermore, both pre- and post-weaning information pertaining to fall-calving cows and their calves grazing E+ is particularly limited. A 3-year study was initiated in April 2000 near Batesville, AR (USA) to investigate the impact of rotational management (twice monthly vs. twice weekly) program and weaning date [mid-April (EARLY) vs. early June (LATE)] on production of fall-calving cow-calf pairs grazing E+ overseeded with ladino ( Trifolium repens L.), and red clover ( Trifolium pretense L), lespedeza ( Lespedeza stipulacea Maxim.), and crabgrass ( Digitaria sanguinalis (L.) Scop.). A secondary objective of the study was to evaluate calf performance both at weaning and after weaning until either breeding of the heifers or slaughter of the steers. Calves weaned later had greater ( P P P P P P ≥ 0.11) from LATE in the other 2 years. Initial and final feedlot BW and gain did not differ ( P ≥ 0.16) among previous treatments in 2 of 3 years. Therefore, carryover effects of weaning date or rotational grazing on calves previously grazing E+ tall fescue may be mitigated during a subsequent backgrounding period such that impacts on subsequent breeding or feedlot performance is minimized.

Fertilizing bermudagrass (Cynodon dactylon L. Pers.) with N can produce large quantities of forage and increase plant N concentrations. Bermudagrass growing on a caged-layer manure-amended site was fertilized with ammonium nitrate at 4 rates (0, 56, 112, and 168 kg N/ha) approximately 1 mo before first and third harvests on May 30 and August 18, 2000, to determine in situ disappearance kinetics of N and neutral detergent insoluble N (NDIN). Five crossbred ruminally cannulated steers (BW = 422 ± 21.0 kg) were used to evaluate in situ disappearance kinetics in a randomized complete block design with a 2 × 4 factorial arrangement. Immediately soluble N (fraction A) and rate of N disappearance increased linearly (P

Bailey, C.R., Daniels, L.B., Coblentz, W.K., Kegley, E.B., McBeth, L.J., Turner, J.E., Wistuba, T.J. and Rosenkrans Jr., C.F. 2007. Evaluation of soft red winter wheat forage yield, nutritive value and tetany hazard as influenced by sampling date and nitrogen fertilization. J. Appl. Anim. Res., 32: 1–6. A study was conducted from December through March using a completely randomized design to evaluate yield, nutritive value and tetany hazard of soft red winter wheat (Triticum aestivum L.) forage as influenced by nitrogen (N) fertilization rate and date of sampling. Dry matter (DM) yield, forage DM, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro, dry matter disappearance (IVDMD), organic matter (OM), calcium (Ca), magnesium (Mg) and potassium (K) were evaluated. Nitrogen fertilization had no effect (P>0.05) on forage yield, OM, ADF, NDF, IVDMD, Ca or Mg. Forage DM (P

The economic impact of rotation frequency (twice weekly vs. twice monthly until time of weaning) and time of weaning (early April vs. 56 d later) was examined for fall-calving cows using a modified put and take grazing strategy implemented to maintain equal grazing pressure across production systems. Cow and/or calf death losses resulted in replacements with either bred cows or cow-calf pairs. While the analysis on heifer calves was limited to sale at time of weaning, steer calves were tracked through the feedlot stage to determine if the time of sale would alter production system recommendations. For the conditions presented in this study, cow-calf producers may be advised that (i) relative to late weaning, early weaned calves did not regain their weight disadvantage observed at time of weaning; (ii) more intensive pasture management (rotating twice weekly rather than twice monthly) was not worth the effort because partial return results for late-weaned steer and heifer calves did not differ statistically by rotation frequency, regardless of sale time; (iii) partial returns were highest for steer calves retained through the finishing stage at the feedlot (regardless of production system) compared with sale at the time of weaning or at the time of placement in the feedlot; (iv) the range of returns or financial risk exposure increased with length of calf ownership. However, use of long-term average prices excluded input price risk from the analysis and output price risk was only partially addressed.

A 4-yr trial was initiated in January 2000 to evaluate cow-calf performance on mixed-species pasture systems consisting of (i) endophyte-infected tall fescue (E+; Festuca arundinacea Schreb.) diluted by approximately 50% with common bermudagrass [Cynodon dactylon (L.) Pers.] and other forages; (ii) endophyte-free tall fescue (E-) overseeded into dormant common bermudagrass; and (iii) orchardgrass (OG; Dactylis glomerata L.) established under the same conditions as E-. The E- and OG pastures were grazed with either twice weekly (2W) or twice monthly (2M) rotation schedules, while pastures with E+ were grazed with 2M only. Actual weaning weights tended to be greater (P = 0.096), and age-adjusted 205-d weaning weights and average daily gain from birth to weaning were greater (P ≤ 0.035) for calves raised on low-toxicity (E - or OG) pastures compared to those raised on E+. Over 4 yr, calves raised on low-toxicity pastures exhibited 22- and 24-kg advantages in actual and 205-d adjusted weaning weights, respectively, compared to those raised on E+. Cows grazing OG and E- pastures exhibited greater (P ≤ 0.021) body weights and body condition scores (BCS) at calving than cows grazing E+ pastures. Furthermore, reductions in body weight and BCS between calving and weaning tended to be greater (P ≤ 0.088) for cows grazing E+ pastures. Calf performance was improved consistently by these low-toxidty pasture systems, but management requirements may limit adaptation by producers.

A systems trial was designed to evaluate forage characteristics within mixed-species pastures consisting of (i) endophyte-infected tall fescue (Festuca arundinacea Schreb.; E+) mixed with common bermudagrass [Cynodon dactylon (L.) Pers.] and other forages; (ii) endophyte-free tall fescue (E-) overseeded into dormant common bermudagrass; and (iii) orchardgrass (OG; Dactylis glomerata L.) established under the same conditions as E-. The E- and OG pastures were grazed with either twice weekly (2W) or twice monthly (2M) rotation schedules, but E+ was grazed only as 2M. Across 41 sampling dates (2000 through 2003) the mean forage mass across all forage systems was 3809 kg ha -1 , and there was an interaction of forage system and sampling date (P = 0.001). In vitro dry matter disappearance (IVDMD) and crude protein (CP) varied (P < 0.0001) with sampling date in seasonal patterns that were generally predictable. Frequencies of tall fescue in E- and E+ pastures increased (P < 0.10) over years, reaching numerical maxima (61 to 72%) at the end of the trial. For OG, frequencies reached numerical maxima of 52 and 42% in 2W and 2M pastures, respectively, but then declined (P < 0.10) over time, ending at 39 and 24%, respectively. At the end of the trial, reinfection of OG pastures by rogue E+ plants reached a numerical maximum frequency of only 10%, and concentrations of total ergot alkaloids in tall fescue plants from E- pastures were only about 25% of those for E+ pastures, thereby suggesting that pasture toxicity can be reduced substantially for at least 5 yr using these alternative forage systems.

‘Common’ and ‘Tifton 44’ bermudagrass [Cynodon dactylon (L.) Pers.] located near Fayetteville and Batesville, AR, respectively, were chosen to evaluate the effects of stockpiling initiation date (August or September), and N fertilization rate (0, 37, 74, or 111 kg N ha 21 )o n the nutritive value of fall-stockpiled bermudagrass. At the Fayetteville location, there were initiation 3 harvest date interactions for acid detergent fiber (ADF, P 5 0.003), hemicellulose (P 5 0.003), cellulose (P 5 0.0003), lignin (P 5 0.007), and crude protein (CP, P 5 0.008) in 2000, and strong interactions (P # 0.001) for all response variables in 2001. Generally, neutral detergent fiber (NDF), ADF, cellulose, and lignin increased over harvest dates for both initiation dates in 2000, although increases for lignin were only numerical (P . 0.05) for the September initiation date. Similar responses were observed for the August initiation date in 2001, but fiber components for the September 2001 initiation date declined over time because of contamination by other winter-annual species. For August initiation dates in 2000 and 2001, in vitro organic matter disappearance (IVOMD) declined linearly (P # 0.002) over harvest dates, reaching respective minima of 330 and 361 g kg 21 . At the Batesville site, an N fertilization effect (P # 0.017) was observed for NDF, ADF, and CP in both 2000 and 2001. A similar effect was observed for lignin (P 5 0.001) and IVOMD (P , 0.0001) in 2000, and for cellulose (P 5 0.0004) during 2001. Fertilization with N at the initiation of stockpiling generally reduced fiber components, and increased CP; however, IVOMD was increased for 2000 only. As observed for the Fayetteville site, most fiber components increased over harvest dates, while IVOMD declined concomitantly. Generally, the nutritive value of stockpiled bermudagrass declines between mid-October and mid-December, and spring-calving beef cows in the Upper South may need to be supplemented with energy to maintain body condition in the late fall or early winter.

Southern crabgrass (Digitaria ciliaris [Retz.] Koel.) is often an undesirable species in field and forage crops, but visual observations suggest that livestock prefer it to many other summer forages. The objectives of this study were to assess the nutritive value of crabgrass sampled weekly between July 11 and August 22, 2001 and then to determine ruminal in situ disappearance kinetics of N and neutral detergent insoluble N (NDIN) for these forages. A secondary objective was to compare these kinetic estimates for crabgrass with those of alfalfa (Medicago sativa L.), bermudagrass (Cynodon dactylon [L.] Pers.), and or-chardgrass (Dactylis glomerata L.) as control hays. All kinetic evaluations were conducted with 5 ruminally cannulated Gelbvieh x Angus x Brangus steers (383 +/- 22.7 kg). Concentrations of N for crabgrass decreased linearly (P < or = 0.002) across sampling dates for leaf, stem, and whole-plant tissues. Conversely, percentages of the total N pool within NDIN and ADIN fractions generally increased over sampling dates in mostly linear patterns. For crabgrass, the immediately soluble portion of the total N pool (fraction A; overall mean = 54.6% of N) was greater (P < 0.001) than for all control hays. Crabgrass exhibited a more rapid N disappearance rate (overall mean = 0.093/h; expressed as a proportion disappearing/h) than that of bermudagrass (0.046/h; P < 0.001), but the disappearance rate for alfalfa N (0.223/h) was considerably faster (P < 0.001) than for crabgrass. The effective ruminal disappearance of N was greater (P < 0.001) for crabgrass (overall mean = 85.4%) than for the alfalfa (83.3%), bermudagrass (72.3%), or orchardgrass (76.0%) control hays. For alfalfa, the ruminal disappearance rate of NDIN (0.150/h) was more rapid (P < 0.001) than for crabgrass (overall mean = 0.110/h); however, the disappearance rate for crabgrass was faster than that for bermudagrass (0.072/h; P < 0.001) or for orchardgrass (0.098/h; P = 0.010). Effective ruminal disappearance of NDIN was greater (P < 0.001) for crabgrass (overall mean = 72.0%) than for the bermudagrass (69.0%) or alfalfa hays (50.5%), but there was no difference (P = 0.865) between crabgrass and orchardgrass (72.1%). Although crabgrass forages exhibited concentrations of total N that were comparable with those of alfalfa and rates of ruminal N disappearance that were < 50% of those for the alfalfa hay control, improvements in N use efficiency relative to alfalfa are questionable because of the excessively large Fraction A for crabgrass.

This study investigated the effects of simulated rainfall on N partitioning and concentrations of degradable (DIP) or undegradable (UIP) intake protein for wilting orchardgrass (Dactylis glomerata L.) and bermudagrass [Cynodon dactylon (L.) Pers.] hays. Orchardgrass forage was wilted to 674, 153, or 41 g kg 21 of moisture (WET-O, IDEAL-O, and DRY-O, respectively) in the field before applying the simulated rainfall (0, 13, 25, 38, 51, 64, or 76 mm). For WET-O, DIP (g kg 21 crude protein [CP]) increased cubically (P 5 0.020) with simulated rainfall, but the overall range of response was small (653–673 g kg 21 CP). Estimates of DIP (g kg 21 CP) for IDEAL-O and DRY-O decreased by 46 and 25 g kg 21 CP, respectively, between the 0and 76-mm rainfall increments; for IDEAL-O, these decreases occurred in a linear (P , 0.0001) pattern, whereas quadratic (P 5 0.009) and linear (P 5 0.029) effects were observed for DRY-O. Bermudagrass forage was field wilted to 761, 400, or 130 g kg 21 of moisture (WET-B, MID-B, and IDEAL-B, respectively) and evaluated similarly. For WET-B and MID-B, DIP (g kg 21 CP) was not affected (P . 0.05) by simulated rainfall. In contrast, quartic (P 5 0.019) and linear (P 5 0.002) effects were observed for IDEAL-B, but these responses were confined primarily to changes between the undamaged (0-mm) control and the initial 13-mm rainfall increment. On a practical basis, concentrations of DIP were, at most, altered only moderately in response to simulated rainfall and relatively little when forages were still too wet to bale.

A grazing study was initiated in April 2000 and continued through three calving and weaning cycles (ending July 2003) to investigate the effects of rotational grazing management (twice monthly [2M] vs. twice weekly [2W]) and weaning date (mid-April [EARLY] vs. early June [LATE]) on production of fall-calving cow-calf pairs (495 +/- 9.6 kg initial BW) grazing Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.) overseeded with legumes and crabgrass. Secondary objectives of the experiment were to monitor differences in quantity and quality of available forage and to evaluate changes in forage species composition. Pastures were dominated by tall fescue throughout the study, and the proportion of basal cover was greater (P < 0.05) in 2M than in 2W pastures. The percentage of legumes was very low across all treatment combinations, but the percentage of crabgrass continued to increase (P < 0.05) linearly and quadratically across years for both summer and fall sampling periods, regardless of rotation or weaning program. In vitro DM disappearance and mineral concentrations varied minimally because of rotation frequency or weaning date. Rotation frequency did not substantially affect (P = 0.11 to 0.97) cow BW, hay offered, milk production, calving interval, calf birth weight, or actual or adjusted weaning weights; however, 2M cows had 0.3 units higher (P < 0.05) BCS at the time of breeding than 2W cows. Calves weaned late had greater (P < 0.05) actual weaning weight and weighed more (P < 0.05) on the LATE weaning date than on the EARLY weaning date, but 205-d adjusted weaning weights did not differ (P = 0.74) across weaning dates. Therefore, rotation frequency and/or weaning date had little effect on forage species composition or forage quality. In addition, the rapid rotation program offered little advantage with respect to animal performance, and weaning fall-born calves grazing endophyte-infected tall fescue pastures at approximately 189 d of age seemed to be detrimental to calf performance compared with delaying weaning until 243 d of age.

Southern crabgrass (Digitaria ciliaris [Retz.] Koel.) is often viewed as an undesirable weed, largely because it encroaches upon field and forage crops, gardens, and lawns. However, visual observations of livestock grazing mixed-species pastures suggest that cattle seem to prefer crabgrass to many other summer forages. The objectives of this study were to assess the nutritive value of crabgrass sampled weekly between July 11, and August 22, 2001, and then to determine ruminal in situ disappearance kinetics of DM and NDF for these crabgrass forages. A secondary objective was to compare these kinetic estimates with those of alfalfa (Medicago sativa L.), bermudagrass (Cynodon dactylon [L.] Pers.), and orchardgrass (Dactylis glomerata L.) control hays. All forages were evaluated in situ using five (383 +/- 22.7 kg) ruminally cannulated crossbred (Gelbvieh x Angus x Brangus) steers. Whole-plant crabgrass exhibited more rapid (P < or = 0.002) ruminal disappearance rates of DM (overall range = 0.069 to 0.084 h(-1)) than did bermudagrass (0.054 h(-1)) and orchardgrass (0.060 h(-1)) hays, but disappearance rates were slower (P < 0.001) for crabgrass than for alfalfa hay (0.143 h(-1)). Effective ruminal disappearance of DM was greater (P < 0.001) for crabgrass (overall range = 69.3 to 75.4%) than for all the control hays. Similarly, disappearance rates of NDF for crabgrass (overall range = 0.069 to 0.086 h(-1)) were more rapid (P < 0.001) than observed for bermudagrass and orchardgrass hays; however, NDF in alfalfa disappeared at a faster (P < 0.001) rate (0.107 h(-1)) than crabgrass. These results indicate that crabgrass offers greater effective ruminal degradability of DM and NDF than orchardgrass or alfalfa of moderate quality. More importantly, it potentially offers faster and more extensive ruminal disappearance than perennial warm-season grasses typically found throughout the southeastern United States, and it should likely support improved performance by ruminant livestock in this region.

Using recently developed technology, balage is often stored in large (1.2 x 1.2 m) round bales that are wrapped in plastic film with an in-line wrapper. The aerobic stability of this fermented forage is important, particularly during winter months when it is fed to livestock or sold as a cash crop. Two types of forage, orchardgrass [Dactylis glomerata L.; 54.4% dry matter (DM)] and wheat (Triticum aestivum L.; 62.4% DM), were packaged in large round bales and wrapped with an in-line wrapper during May 2002. Twenty-one bales of each balage type were unwrapped and exposed to air on Dec. 10, 2002 for 0, 2, 4, 8, 16, 24, or 32 d (ambient temperature range = 0.6 to 19.4 degrees C) to evaluate aerobic stability. For both orchardgrass and wheat balage, final bale weight, concentration of DM, and pH were not affected by exposure time. Across both balage types, DM recoveries wereor = 97% for all bales, indicating that both balage types were very stable when exposed to air. For orchardgrass balage, exposure time had no effect on concentrations of NDF, ADF, hemicellulose, cellulose, or lignin, thereby indicating that little deterioration occurred. Similarly, no contrast relating any fiber component with exposure time was significant for wheat balage. Concentrations of crude protein (CP) were not affected by exposure time for wheat balage, but there was a tendency for exposed orchardgrass bales to have greater concentrations of CP than bales sampled on d 0. Exposure time had no effect on 48-h in situ digestibility of DM for wheat balage, but there was a tendency for a linear increase with exposure time for orchardgrass balage. However, the overall range (78.2 to 80.5%) over the 32-d exposure period was very narrow, and this response is probably of limited biological significance. Generally, concentrations of fermentation acids were low, primarily because of the high concentration of DM within these balages, and only minimal changes in these acids were observed over the exposure interval. These results suggest that the balage evaluated in this trial during winter conditions was very stable after exposure to air for up to 32 d. This should allow for considerable flexibility with respect to feeding, transport, and marketing of balage during winter months without significant aerobic deterioration.

Throughout much of the southeastern USA, hay harvest can be complicated by a high probability of rainfall events that may cause damage to the resultant hay crop. The objectives of this study were to investigate the effects of simulated rainfall and two postrainfall drying methods on losses of dry matter (DM) and changes in nutritive value for wilting orchardgrass (Dactylis glomerata L.) and bermudagrass [Cynodon dactylon (L.) Pers.] forages. Orchardgrass was wilted to moisture concentrations of 674 (WET), 153 (IDEAL), and 41 (DRY) g kg - 1 and subjected to 0,12, 25, 38, 51, 64, or 76 mm of simulated rainfall from a custom-built rainfall simulator. For IDEAL orchardgrass, DM loss reached a maximum of 88 g kg - 1 when 76 mm of simulated rainfall was applied. Dry matter loss, total N, and all fiber components except hemicellulose increased with rainfall amount, exhibiting single or multiple polynomial effects (P ≤ 0.048) in each case; however, responses were not consistent across these response variables. A second study was conducted with bermudagrass using similar techniques, except that the forage contained 761 (WET), 400 (MID), and 130 (IDEAL) g kg - 1 of moisture when simulated rainfall was applied. For IDEAL bermudagrass forage, DM losses increased in linear (P = 0.001) and quadratic (P = 0.003) relationships with simulated rainfall, but the maximum DM loss was only 21 g kg - 1 . For both forages, DM loss and deleterious changes in nutritive value generally increased with rainfall amount, but these responses appeared to be much greater for orchardgrass.

Previous methodologies to measure losses of dry matter (DM) in wilting hays subjected to natural or simulated rainfall have relied generally on gravimetric techniques, resulting in variable and questionable estimates of DM loss. The objective of this study was to evaluate the use of fiber components and acid detergent insoluble ash (ADIA) as internal plant markers for accurately predicting losses of DM in bermudagrass [Cynodon dactylon (L.) Pers.] and orchardgrass (Dactylis glomerata L.) forages that were damaged by simulated rainfall. For both forages, concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HEMI), cellulose (CELL), lignin, and ADIA generally increased with the amount of simulated rainfall in primarily linear patterns. Recoveries of all internal markers were high (≥952 g kg -1 ) and were not affected by simulated rainfall for either forage (P ≥ 0.06). Predicted losses of DM increased in primarily linear patterns with simulated rainfall for both forages when concentrations of NDF, ADF, HEMI, CELL, and ADIA were used as internal markers. Linear regressions of predicted losses of DM on values determined gravimetrically were good (r 2 ≥ 0.73; P ≤ 0.03) when concentrations of any fiber constituent or ADIA were used to calculate losses of DM; however. NDF was an especially effective internal marker (Y = 1.12X - 5; r 2 = 0.97; P < 0.01).

Two case studies were conducted on producer farms in northwest Arkansas to assess degradable intake protein (DIP) and undegradable intake protein (UIP) in forages grown throughout the region. In Case Study 1, DIP was greater (P 0.05) in warm-season pastures when DIP was expressed as a percentage of CP. In Case Study 2, N fertilization in April and July at two producer sites (Latta and Stephens) increased concentrations of CP for subsequent harvests in primarily linear (P 0.05) for a mid-summer (July 7) harvest that received no fertilization. In harvests immediately following fertilization, DIP increased; the linear term was significant (P≤0.004) in each case, but it was coupled with quadratic or cubic effects in some harvests. For the second harvest at each site, DIP was not affected (P>0.05) by residual effects of the initial application of N fertilizer in April. The size of the UIP pool also increased linearly (P≤0.002) immediately following N fertilization in three of four harvests, but the magnitude of these responses was small compared with those observed for DIP.

Relatively little is known about the combined effects of spontaneous heating and natural rainfall on the feeding value of ‘Kentucky 31’ tall fescue (Festuca arundinacea Schrieb.) hay infested with the fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Glenn, Bacon, and Hamlin comb. nov.). A digestion trial utilizing a 4 × 4 Latin square design was initiated to determine the effects of both natural rainfall before baling and spontaneous heating during storage on the voluntary intake, digestibility, in situ disappearance kinetics, and ruminal fermentation characteristics of tall fescue hay consumed by four 227 ± 20.5 kg steers. The four tall fescue hays utilized in this experiment were baled at 99 (low, L), and 225 g/kg (high, H) moisture prior to rainfall, and at 246 g/kg moisture after a 23 mm rainfall event (H–R) and at 93 g/kg moisture after a total accumulation of 72 mm of rain (L–R). Daily voluntary intake of the total diet, and dry matter (DM) and organic matter (OM) intakes of hay (g/kg body weight) were greater (P ≤ 0.032) for steers consuming hays baled without rainfall prior to baling than for those receiving rainfall during the wilting period. However, hays altered by rain had greater (P ≤ 0.033) apparent digestibilities of DM, OM, NDF, and ADF than did hays baled without rainfall. Effective in situ disappearance of DM and N was poorer (P ≤ 0.033) for hays altered by rainfall, spontaneous heating, or both (H, H–R, and L–R) than for L hay, but effective NDF disappearance was not affected by treatment (P ≥ 0.361). Ruminal fermentation characteristics and passage kinetics varied little between the four diets. Although hay receiving no rainfall had slightly better characteristics of nutritive value and in situ degradation than hays altered by rainfall, apparent total tract digestibilities were higher for hays altered by rainfall. While depressed total tract digestibilities in hay baled without rainfall were clearly associated with higher voluntary intakes, statistically significant decreases in ruminal or total tract retention times could not be established clearly.

Common bermudagrass [Cynodon dactylon (L.) Pers.] was harvested from two producer sites (Latta and Stephens) with high soil-test P (286 and 153 ppm, respectively) to assess the effects of N fertilization on P uptake and potential removal in hay or silage. Ammonium nitrate was applied in split applications each year at rates totaling 0, 56, 112, 168, 224, 280, or 336 kg/ha of actual N. At the Stephens site in Yr 1, cumulative DM yield increased linearly (P 0.10) between concentration of P and N fertilization rate (overall mean = 0.40%), but concentrations of P declined in linear (P

Autumn stockpiling is a management technique in which forage is allowed to accumulate throughout the late summer and early fall for subsequent grazing throughout the late fall and winter. Well-established stands of common and 'Tifton 44' bermudagrass [Cynodon dactylon (L.) Pers.] located at Fayetteville and Batesville, AR, respectively, were chosen to evaluate the effects of stockpiling initiation date (August or September) and N fertilization rate (0, 37, 74, or 111 kg N ha -1 ) on the canopy height and dry matter (DM) yield potential of autumn-stockpiled bermudagrass forage. Within year, DM yield increased linearly (P ≤ 0.008) with N fertilization rate at Fayetteville in 2001 and in Batesville during both years. For August initiation dates, DM yield declined linearly (P ≤ 0.007) with harvest date at both sites during both years; however, cubic responses (P ≤ 0.024) also were observed at both sites in 2000 but not (P ≥ 0.076) in 2001. For September initiation dates, DM yield exhibited less consistent patterns over harvest dates, but responses were cubic (P ≤ 0.053) over time for all four site-years. Tests of homogeneity for regressions of DM yield on canopy height for individual site-years indicated there were differences for the intercepts (P < 0.001) and linear coefficients (P < 0.001) and a tendency for the quadratic coefficients (P = 0.063) to differ. Quadratic equations are not suitable for producer use; therefore, a combined linear model for all data (N = 512) was determined, Y = 146x - 838 (P < 0.001; r 2 = 0.762), which may address the need for a quick estimator of available forage.

Ruminal in situ disappearance kinetics of nitrogen (N) in forages are frequently evaluated in confined animals, but there have been relatively few attempts to obtain these kinetic estimates from grazing animals. Our objectives were to evaluate the effects of harvest technique and sampling date on the in situ N disappearance kinetics and nutritive value of wheat ( Triticum aestivum L.) forage, and to compare in situ disappearance kinetics of N for these forages when the experimental steers were housed in confinement with those obtained from steers grazing wheat pasture. Wheat forages were harvested on three dates (March 6, March 27, and April 11, 2000) using five sampling techniques. These included three clipping techniques (whole plant, random pluck, and top half) and two evaluations of masticates (oven dried at 50 °C or lyophilized). Disappearance kinetics of N for the 15 experimental forages were evaluated by the in situ technique using five 393±54.4 kg crossbred steers that were offered an alfalfa based ( Medicago sativa L.) diet and were housed in confinement. Subsequently, this evaluation was repeated in five 448±48.6 kg crossbred steers grazing wheat pasture during March 2001. Kinetic parameter estimates obtained from grazing steers were regressed on those obtained from confined steers. A slope of unity and an intercept of zero is indicative of agreement between the two methods. For lag time and fractions A and B (i.e., portions of total N that are immediately soluble and that disappear at a measurable rate, respectively), the slopes and intercepts did not differ ( P ≥0.126) from unity and zero, respectively. For the disappearance rate ( K d ), the slope (0.92) did not differ ( P =0.408) from unity, but the intercept (0.027) was higher ( P =0.026) than zero. The slope (1.23) and intercept (−24.3% of N) for estimates of effective ruminal disappearance of N differed ( P ≤0.033) from unity and zero, respectively, but these differences were largely an artifact of the different ruminal passage rates used to calculate effective disappearance. From a practical standpoint, the in situ disappearance kinetics of N for these wheat forages were not altered substantially when they were obtained from grazing steers.

Common bermudagrass [Cynodon dactylon (L.) Pers.] growing on a poultry layer manure-amended site (layer manure was last applied in 1999) was fertilized with ammonium nitrate at four rates (0, 56, 112, and 168 kg N ha−1) at approximately 1 month before first and third harvests on 30 May and 18 August 2000 to evaluate forage concentrations of S and Mo, and concentrations and ruminal disappearance of Fe, Zn, and Cu. Five crossbred ruminally cannulated steers (422±21.0 kg BW) were used to evaluate ruminal disappearance of Fe, Zn, and Cu from these forages in situ in a randomized complete block design with a 2×4 (harvest date×N fertilization rate) factorial arrangement of treatments. Forage S concentrations decreased linearly (P=0.02) with increasing N application on both harvest dates, but Fe, Zn, Cu, and Mo concentrations did not differ (P≥0.24) across N fertilization rates. The intercepts for the regressions of S, Zn, Cu, and Mo concentrations on N fertilization rate were higher (P

Minerals are essential nutrients for animals as primordial elements for structural tissues and metabolic reactions. Forages are considered an important source of minerals for ruminants, but forage mineral concentrations may vary across the growing season due to several factors such as forage species and fertilization levels. Common bermudagrass [Cynodon dactylon (L.) Pers.] growing on a poultry layer manure-amended site was fertilized with ammonium nitrate at four rates (0, 56, 112, and 168 kg N/ha) approximately 1 month before the first and third harvests (30 May and 18 August 2000, respectively) to evaluate those effects on forage concentration and ruminal disappearance of Ca, P, Mg, and K. Five crossbred ruminally cannulated steers (422 ± 21.0 kg BW) were used to evaluate these forages in situ in a randomized complete block design with a 2 x 4 (harvest date x N fertilizationrate) factorial arrangement of treatments. Forage P content decreased (P < 0.01) with increasing N fertilization on 18 August, while forage Mg increased (P < 0.01) and forage Ca content tended (P = 0.08) to increase with increasing N fertilization on both harvest dates. Approximately, 992 g/kg of the K disappeared immediately (fraction A) from the bags compared with approximately 821, 718, and 476 g/kg of Mg, P, and Ca, respectively. Fraction A, fraction B (the fraction disappearing at a measurable rate), and effective ruminal disappearance of Ca, P, Mg, and K were affected by linear or quadratic interactions between N fertilization and harvest date. Effective P disappearance increased linearly (P < 0.05) on 30 May and decreased quadratically (P < 0.01).

Relatively little is known about the combined effects of rain damage and spontaneous heating on the storage characteristics and nutritive value of tall fescue (Festuca arundinacea Schreb.) hay. Objectives were to assess effects of these variables in five management situations. ‘Kentucky 31’ tall fescue infested with the fungal endophyte (Neotyphodium coenophialum [Morgan-Jones & Glenn, Bacon, and Hamlin comb. nov.]) was packaged in conventional rectangular bales at 99 g/kg (low, L), 164 g/kg (ideal, I), and 225 g/kg (high, H) of moisture prior to rainfall, and at 246 g/kg of moisture after a 23 mm rainfall event (H–R) and at 93 g/kg of moisture after a total accumulation of 72 mm of rain (L–R). Concentrations of neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and lignin immediately after baling increased (P≤0.017) with rain damage, but concentrations of total N and fiber-associated N components were little affected. Immediately after baling, the in situ dry matter (DM) disappearance for L–R hay was 32–44 g/kg lower (P=0.0001) than observed for hays baled without rain damage. After a 40–45-day storage period, L and I hays had a 31–36 g/kg advantage for in situ DM disappearance over hays damaged by spontaneous heating (H), rainfall (L–R), or both (H–R). Generally, the effects of a single 23 mm rainfall event on the nutritive value of tall fescue hay was relatively small, but damage increased substantially with multiple rainfall events.

Spontaneous heating reduces forage quality and nutrient digestibility in stored alfalfa ( Medicago sativa L.) and cool-season grasses. However, research describing the impact of spontaneous heating on disappearance kinetics of warm-season grasses is limited. Five crossbred ruminally cannulated steers were used in a randomized complete block design to determine the impact of spontaneous heating during the curing process on in situ disappearance kinetics of bermudagrass hay. Bermudagrass hays were baled at various moisture levels and bale densities that resulted in spontaneous heating that produced 5, 119, 201, 273, or 401 heating-degree days (HDD; >35 °C) during a 60-day storage period. Hays were evaluated for rumen dry matter (DM), neutral-detergent fiber (NDF), N, and neutral-detergent insoluble nitrogen (NDIN) disappearance kinetics. The immediately soluble DM fraction and effective ruminal DM disappearance generally decreased ( P P K d ) was faster ( P K d for NDF was faster ( P P K d for N was faster ( P P K d for NDIN was faster ( P P

Nutrient composition and in situ dry matter (DM) and neutral detergent fiber (NDF) degradation of bermudagrass [Cynodon dactylon (L) Pers.] may vary with different management and environmental factors. This study evaluated nutritional value and in situ degradation characteristics of DM and NDF for bermudagrass, a perennial, warm-season grass. Bermudagrass growing on a poultry layer—litter—amended site was fertilized with ammonium nitrate at four rates (0, 56, 112, and 168 kg N ha−1) on 28 April and 19 July 2000, then harvested on 10 May and 18 August 2000. Five crossbred ruminally-cannulated steers (422±21.0 kg body weight (BW)) were used in a randomized complete block design with a 2×4 (harvest date×N fertilization rate) factorial arrangement to determine in situ DM and NDF degradation kinetics. Quadratic relationships were detected between N fertilization rates and N concentration in the plant when harvested on 30 May (y=0.0001x2+0.009x+27; P 0.05) across N fertilization rates. The undegraded DM fraction (fraction C) declined (P

Limited information is available describing digestive kinetics of crude protein (CP) in stockpiled bermudagrass ( Cynodon dactylon (L.) Pers.) during late fall and early winter. ‘Greenfield’ bermudagrass was stockpiled at two sites following summer hay or pasture management, and samples were taken at 4-week intervals under caged exclosures (UNGRAZED) and outside exclosures (GRAZED) between 17 October 1997 and 9 January 1998. Forage samples were subsequently incubated in situ in five ruminally cannulated, crossbred steers to determine effects of fall harvest date and previous summer management on in situ degradation kinetics of forage CP. At the hay site, concentrations of total plant CP declined ( P −1 ) and 12 December (119.4 g kg −1 ), but concentrations of CP did not differ ( P >0.05) on the 17 October and 9 January harvest dates. From the pasture site, concentrations of total CP for UNGRAZED forages did not change ( P >0.05) throughout the trial. In situ degradation rates of CP from the hay site were not different ( P >0.05) for UNGRAZED forages on 17 October and 9 January (overall mean=0.056 h −1 ). The ruminal degradation of CP decreased ( P −1 CP between 14 November and 12 December, but did not change during the first and last sampling intervals. At the pasture site, rates of CP degradation increased ( P −1 ) and 9 January (0.080 h −1 ) due to the presence of immature, winter annual weeds. Similarly, the ruminal degradation of CP increased ( P −1 ) and 9 January (624 g kg −1 ) in response to winter annual weed presence. Ruminal availability of CP in stockpiled bermudagrass decreases as the dormant forage ages, but may be adequate to meet the minimum CP requirements of dry, pregnant beef cows.

Relatively little is known about storage of wet (>200 g kg -1 moisture) bermudagrass [Cynodon dactylon (L.) Pers.] hay. Our objective was to assess the changes in nutritive value of bermudagrass hay as a function of hay moisture, storage time, and spontaneous heating. Greenfield' bermudagrass was grown on a Pickwick silt loam soil (fine-silty, mixed, semiactive, thermic Typic Paleudult) and packaged in conventional rectangular bales at 219, 265, and 302 g kg -1 moisture [low-moisture (LM), medium-moisture (MM), and high-moisture (HM) bales, respectively]. Concentrations of most fiber and fiber-associated N components increased (P 200 g kg -1 moisture deteriorates during storage, and the greatest deterioration occurs during the first 12 d after baling.

Estimates of rumen degradable or escape N are an important component of current nutritional models for feeding livestock, but attempts to estimate these fractions for bermudagrass [Cynodon dactylon (L.) Pers. have been limited, and the relationship between concentrations of these fractions and spontaneous heating during bale storage has not been evaluated. The objectives of this study were to (i) assess the relationship between rumen escape or degradable N and spontaneous heating in bermudagrass hays harvested from the same site during 1998 and 1999 and (ii) correlate estimates of rumen escape and degradable N with other measures of forage nutritive value that are evaluated commonly. A preparation of Streptomyces griseus protease was utilized in an in vitro laboratory procedure to quantify rumen degradable N in hays that heated spontaneously during storage in small haystacks. Maximum temperatures in these bales ranged from 37.1 to 69.8°C over 2 yr. Rumen escape N for 40 hays ranged from 407 to 613 g kg -1 N and increased linearly (P 0.05) for specific harvest years.

Wheat (Triticum aestivum L.), oat (Avena sativa L.) and rye (Secale cereale L.) were overseeded into a dormant bermudagrass (Cynodon dactylon (L.) Pers.) sod and harvested on six dates throughout the spring. Plant growth stage was documented for each forage on each harvest date, and harvested forages were subsequently evaluated for forage quality characteristics. Four ruminally cannulated steers were used to evaluate disappearance kinetics of nitrogen (N) by an in situ method. All forages had high concentrations of N (≥31.1 g kg−1 DM) throughout harvest dates in March. By 15 April, rye had reached a substantially more advanced growth stage than either wheat or oat. This trait, coupled with the concurrent taller growth habit, caused concentrations of N in rye to decline (P

Conserving hay at moisture concentrations 200 g kg 1 is known to cause spontaneous heating and negative effects on forage nutritive value. While these relationships have been evaluated extensively for alfalfa (Medicago sativa L.), less research has evaluated these factors in warm-season grasses, specifically bermudagrass [Cynodon dactylon (L.) Pers.]. In this study, Greenfield' bermudagrass was grown on a Pickwick silt loam soil (fine-silty, mixed, semiactive, thermic Typic Paleudult) and packaged in conventional rectangular bales at five concentrations of moisture (178, 208, 248, 287, and 325 g kg ') and at high and medium bale densities (overall means = 208 and 186 kg m 3 , respectively). Bale density had little effect on forage nutritive value after storage. Furthermore, hale density had no effect (P > 0.05) on indices of spontaneous heating (heating degree days 35°C, maximum temperature, and 30-d average temperature), visual evalualion of mold, and dry matter (DM) recovery. Positive linear relationships occurred between concentrations of fibrous forage components and indices of spontaneous heating; coefficients of determination (r 2 ) statistics were similar for each index of spontaneous heating that was used as the independent variable in these linear regressions. Concentrations of acid detergent insoluble N and neutral detergent insoluble N expressed on a DM basis were positively related to measures of spontaneous heating in close linear relationships (r 2 ≥ 0.80). Regressions of other N fractions on measures of spontaneous heating exhibited lower coefficients of determination, but generally had significant slopes. Results of this study indicate that N in bermudagrass is very susceptible to reductions in bioavailability through heat damage during bale storage, and that this damage is increased with increases in initial bale moisture.

The influence of item familiarity upon memory span was examined in adults and children aged 5, 7, and 10 years by comparing the recall of words and nonwords. Using a probed recall task, both item recall and position recall were tested. The effect of familiarity upon item recall was found to develop with age, from no effects in the 5-year-olds to significant effects in the older children and adults. By contrast, no effect of familiarity was found at any age when recall of position was required. Dissociations between word length effects and familiarity effects supported the conclusion that the familiarity effect does not result from rehearsal. Several explanations for the source of the familiarity effect were examined, and the familiarity effect was attributed to a strategic redintegration or reconstruction process, which is necessary for item recall but not for position recall.

Eastern gamagrass [Tripsacum dactyloides L.] is a native, warm-season, perennial, bunch-type grass adapted generally to moist sites throughout much of the eastern United States. Nitrogen concentrations of eastern gamagrass will normally exceed 20 g/kg at growth stages (boot and anthesis) that produce reasonable yields. With moderate N fertilization, concentrations of N approaching 32 g/kg are realistic in whole-plant tissue harvested at boot stage in the upper Midwest. Recent studies suggest that high proportions (>50%) of this N are insoluble in neutral detergent (NDIN), thereby implying association with the cell wall. In situ studies in Kansas have shown that the potential extent of ruminal N degradation for gamagrass harvested at boot stage is comparable with that of high quality legumes, but degradation occurs at slower rates; generally, similar trends have been observed for in situ disappearance of DM and fibrous components. Increasing plant maturity appears to limit extent primarily, but not the rate, of degradation for these plant components. Concentrations of NDF are generally high (>600 g/kg), even at immature growth stages; this observation is consistent with findings for other warm-season grasses. In studies conducted throughout the mid South, researchers report that ADG ranged between 0.5 and 1.0 kg/d for steers continuously grazing eastern gamagrass pastures. Daily gains are likely to be reduced as days on pasture increase. Mounting evidence suggests that gamagrass grown in the Midwest demonstrates better quality characteristics than that grown in the Southeast.

We evaluated the potential of sex pheromones to disrupt moth communication and mating of Pandemis leafrollers (likely P. pyrusana Kearfott). The sex pheromone of P. pyrusana, 94:6 (Z)-11-tetradecenyl acetate (Z11–14:Ac): (Z)-9-tetradecenyl acetate, was compared with Z11–14:Ac alone, (E)-11-tetradecenyl acetate (E11–14:Ac) alone, and a 94:6 blend of Z11–14:Ac and (Z)-11-tetradecanal in replicated trials in 0.1-ha plots. All blends significantly reduced moth captures in lure-baited traps and mating of tethered, virgin females. No significant differences were found among pheromone blends, except trap catches in plots treated with E11–14:Ac were significantly higher than in the other pheromone-treated plots. No significant differences in moth catch were found in plots treated with 250–1,000 dispensers per hectare releasing the Pandemis pheromone blend. The percentage of disruption in treated versus untreated plots was not related to the mean dispenser emission rate measured over 2-wk time periods for dispensers releasing either the Pandemis pheromone or Z11–14:Ac alone. However, percentage disruption in plots treated with pheromone was significantly and negatively related to population density measured as moth catch in the untreated plots. Larger orchard trials are needed to evaluate the efficacy and economics of using 500–700 dispensers per hectare loaded with Z11–14:Ac to manage Pandemis.

In mares, dioestrous FSH profiles based on once-a-day sampling are variable; however, the pulsatility of plasma FSH, which has been suggested by limited windows of intensive sampling, may contribute to this variability. Jugular blood from six mares was sampled at 4 h intervals throughout an ovulatory cycle to determine cyclic FSH and LH patterns more accurately and to measure gonadotrophin pulse frequency during dioestrus. Synchronous pulses of FSH and LH occurred regularly in all mares between day 4 and day 12 (ovulation = day 0) with a mean (+/- SEM) frequency of 1.9 +/- 0.1 (FSH) or 1.6 +/- 0.1 (LH) pulses day-1. LH pulse amplitude declined (P < 0.0001) between day 4 and day 10, but FSH pulse amplitude remained large and stable, dipping slightly but not significantly on day 6. Daily mean FSH concentrations exceeded (P < 0.0001) early oestrous values between day 4 and day 5, and between day 7 and day 10. However, significantly different patterns were obtained when once-a-day sampling was simulated by selecting samples collected at 08:00 h or noon. LH was higher during the periovulatory surge than during dioestrus (P < 0.0001) and profiles were similar whether daily means or selected samples were used. It is concluded that: (1) the marked pulsatility of plasma FSH during dioestrus makes once-a-day sampling misleading for determining FSH profiles; (2) the dioestrous pattern of large, slow FSH pulses was consistent among mares, unlike that of the daily mean FSH profiles; and (3) no discrete FSH 'surges' were observed during dioestrus, although FSH pulse amplitude tended to undergo alternate increases and decreases. A period of higher amplitude FSH pulses preceded ovulation by 10.2 +/- 0.7 days, which corresponds to the approximate time the ovulatory follicle emerges. Therefore, it is possible that the signal for follicular recruitment in mares is intermittent excursions of plasma FSH above a threshold value.

The role of sphingomyelin-derived second messengers in progesterone-induced reinitiation of the meiotic cell cycle of Xenopus laevis oocytes was investigated. A brief treatment of defolliculated oocytes with sphingomyelinase (Staphylococcus aureus) was sufficient to induce maturation as measured by H1 kinase activity and germinal vesicle breakdown (GVBD). Pretreatment with cycloheximide inhibited sphingomyelinase-induced GVBD demonstrating a requirement for protein synthesis. Microinjection of ceramide or sphingosine, potential products of sphingomyelin hydrolysis, were capable of inducing GVBD in the absence of hormone. Metabolic labeling studies suggested the conversion of sphingosine to ceramide was necessary for sphingosine-induced GVBD. Additionally, fumonisin b1, an inhibitor of sphingosine N-acyltransferase, blocked sphingosine-induced GVBD demonstrating that ceramide is the more proximal biologically active metabolite. Treatment of oocytes with progesterone, the physiological inducer of oocyte maturation, resulted in a time- and concentration-dependent increase in the mass of ceramide and decrease in the mass of sphingomyelin through activation of a Mg(2+)-dependent neutral sphingomyelinase. These observations suggest that the generation of ceramide from sphingomyelin is part of the signal transduction pathway activated in response to progesterone and that the increase in ceramide is likely to be functionally important in resumption of the meiotic cell cycle.

Cell cycle progression for postembryonic cells requires the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R), the enzyme which catalyzes the production of the isoprenoid precursor, mevalonate. In this study, we examine the requirements of HMG-R activity for cell cycle progression during the meiotic and early mitotic divisions using oocytes and dividing embryos from the surf clam, Spisula solidissima. Using two different inhibitors of HMG-R, we find that the activity of this enzyme appears to be required at three distinct points of the cell cycle during meiosis. Depending on the stage at which these inhibitors are added to synchronous clam cultures, a reversible cell cycle block is triggered at the time of activation or at metaphase of either meiosis I or II, whereas there is not block to the mitotic cell cycle. Inhibition of HMG-R activity in activated oocytes does not affect the transient activation of p42MAPK but results in a block at metaphase of meiosis I that is accompanied by the stabilization of cyclins A and B and p34cdc2 kinase activity. Our results suggest that metabolites from the mevalonate biosynthetic pathway can act to influence the process of activation, as well as the events later in the cell cycle that lead to cyclin proteolysis and the exit from M phase during clam meiosis.

Both Hall and drift in-plane mobilities have been measured in compressively strained p-type Si/sub 1-x/Ge/sub x/ layers grown by both chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). Measurements were taken over the boron doping range of 10/sup 18/ cm/sup -3/ to 10/sup 20/ cm/sup -3/ with Ge contents of 0/spl les/x/spl les/0.22. The apparent drift mobility is found to increase with increasing Ge content, whereas the Hall mobility decreases for the same samples at all doping levels studied. The Hall factor decreases with increasing Ge content, which may be due to additional scattering mechanisms introduced by Ge along with changes in the valence band structure as a result of strain. In this study we also provide the first report of Hall mobility measurements of deuterium-passivated, heavily doped Si. >

Self-aligned SiGe/Si bipolar transistors have been fabricated using a single-polysilicon, double-diffused process with the base in a graded SiGe layer to improve base transit time. To remain compatible with homojunction bipolar technology, undoped SiGe base and Si emitter layers were deposited by selective epitaxy at temperatures of 700-750/spl deg/C in a commercial epitaxial reactor. Maximum cutoff frequencies of 40 and 50 GHz were observed for devices with collector-emitter breakdown voltages (BV/sub CEO/) of 4.2 and 3.0 V, respectively. Preliminary results indicate that the addition of Ge to the base of these transistors did not degrade the long-term device reliability. >

Plexiform layer synaptic and photoreceptor cell components were investigated in retinas of Royal College of Surgeons (RCS) dystrophic rats transplanted with normal retinal pigment epithelial (RPE) cells by immunocytochemistry using previously characterized monoclonal antibodies. In retinas of normal adult rats and RPE-cell transplanted retinas of 4 month-old RCS rats, HNK-1, a marker for a carbohydrate of the neural cell adhesion molecule (N-CAM), was detected immunocytochemically in the inner and outer plexiform layers and ganglion cell bodies and their axons. HNK-1 was also detected in the inner plexiform layer of nontreated retinas of 4 month-old RCS rats, but was reduced to scattered patches in the outer plexiform layer. In addition, immunoreactivity for the SVP-38 antibody recognizing synaptophysin was found in both plexiform layers of normal adult rat retinas and RPE-transplanted retinas of 4 month-old RCS rats. Furthermore, photoreceptor cell bodies and their inner and outer segments were immunostained for the opsin monoclonal antibody RET-P1 in retinas of normal adult rats and RPE-cell transplanted retinas of 4 month-old RCS rats. However, in nontreated retinas of 4 month-old RCS rats, only immunostained debris material was detected. These results strongly suggest that normal RPE transplants not only rescue photoreceptor cells in RCS rats, but also maintain an essential functional capacity, in this case, synaptic components in the plexiform layers. © 1993 Wiley-Liss, Inc.