Optical coherence tomography with a Fizeau interferometer configuration

We report the investigation of a Fizeau interferometer-based OCT system. A secondary processing interferometer is necessary in this configuration, to compensate the optical path difference formed in the Fizeau interferometer between the end of the fibre and the sample. The Fizeau configuration has the advantage of 'downlead insensitivity', which eliminates polarisation fading. An optical circulator is used in our system to route light efficiently from the source to the sample, and backscattered light from the sample and the fibre end through to the Mach-Zehnder processing interferometer. The choice of a Mach- Zehnder processing interferometer, from which both antiphase outputs are available, facilitates the incorporation of balanced detection, which often results in a large improvement in the Signal-to-Noise ratio (SNR) compared with the use of a single detector. Balanced detection comprises subtraction of the two antiphase interferometer outputs, implying that the signal amplitude is doubled and the noise is well reduced. It has been discerned that the SNR drops when the refractive index variation at a boundary is small. Several OCT images of samples (resin, resin + crystals, fibre composite) are presented

Inversely Unstable Solutions of Two-Dimensional Systems on Genus-p Surfaces and the Topology of Knotted Attractors

In this paper, we will show that a periodic nonlinear, time-varying dissipative system that is defined on a genus-p surface contains one or more invariant sets which act as attractors. Moreover, we shall generalize a result in [Martins, 2004] and give conditions under which these invariant sets are not homeomorphic to a circle individually, which implies the existence of chaotic behaviour. This is achieved by studying the appearance of inversely unstable solutions within each invariant set.Comment: 19 pages with 20 figures, AMS La-TeX, to be published in International Journal of Bifurcation and Chao

Conceptus Competition for Nutrients in the Porcine Uterus: Different Strategies Exhibited by the Meishan and Yorkshire Pig Breeds

Previous research from our laboratory demonstrated that Meishan conceptuses develop more slowly and synchronously to day 30 of gestation than conceptuses of U.S. pig breeds. Furthermore, the reduced size of the Meishan conceptus on day 30 allows more Meishan than Yorkshire conceptuses to occupy the same amount of limited uterine space. As a result, Meishan litter size is significantly larger than that of U.S. pig breeds (13−14 vs. 9-10 piglets/litter). An additional consistent, but unexpected, finding in the Meishan pig was the observation that there was significantly greater amounts of unoccupied uterine space in the Meishan than the Yorkshire female at term. We previously demonstrated that an additional strategy of the Meishan female to increase fecundity was to super-vascularize its placental membranes so that oxygen and nutrient transfer from the sow could be accomplished over a reduced surface area, negating the necessity of further placental growth. These data suggested that when a Meishan conceptus dies, the placenta of its neighbors need not grow into this newly vacated space, whereas the Yorkshire conceptus might increase the size of its less vascular placenta to use the opportunity. Therefore, it was our objective to confirm that Yorkshire conceptuses, but not Meishan conceptuses increase their placental size when adjacent conceptuses are experimentally destroyed on day 40 of gestation. To accomplish this objective, pregnant Meishan and Yorkshire females were laporatomized on day 40. One uterine horn was randomly chosen to be receive alternative fetal crushing (i.e., every other fetus in the horn was crushed by mechanical pressure), whereas the other uterine horn served as the control horn. At slaughter on day 111 of gestation (term = 114 days), we found no differences in fetal weight between the control and treated horns regardless of breed. Similarly, there was no difference in placental weight or surface area or implantation site length (the length of placental attachment in the uterine horn) between the control and treated horns in the Meishan. In contrast, however, there was a marked increase in placental weight and surface area, as well as implantation site length for conceptuses in the treated horn of the Yorkshire gilts versus the control horn. Furthermore, the unoccupied spaces between Meishan conceptuses in the treated horn were 2-fold greater than for conceptuses in the control horn, whereas there were no differences in the length of unoccupied spaces between conceptuses in the Yorkshire’s control or treated horns. These data suggest that in the Meishan treated horn, conceptuses do not use this extra space as effectively as conceptuses in the Yorkshire treated horn. The inability of Meishan placenta to grow into adjacent unoccupied spaces may not be detrimental to conceptus survival due to its greater ability to increase vascular density in response to increasing fetal demands. If U.S. pig breeds have the potential to increase placental vascularity, rather than increase in placental size to nourish the growing fetuses, the potential exists for increasing litter size due to a decrease in uterine competition throughout gestation

Effect of Estradiol-17β on Placental Size

Meishan embryos transferred to recipient females on day 2.5 are larger, contain greater numbers of trophectoderm cells, and secrete greater amounts of estradiol-17β when gestated in a Yorkshire compared with Meishan uterus to day 12. Additionally, placentae of Meishan conceptuses are larger when gestated in a Yorkshire compared with Meishan uterus throughout gestation. Embryonic estradiol-17β secretion during elongation on day 12 to 13 of gestation is temporally associated with endometrial secretion of growth factors, including IGF-I, which has been shown to increase mitotic rate in the trophectoderm of pig embryos. This experiment was conducted to determine if estradiol-17β administration to Meishan females at the time of conceptus elongation would increase placental size at term. Meishan females (n=12) were checked twice daily for estrus (0700 and 1900), and each bred to a Meishan boar at 0 and 24 h after the onset of estrus (day 0). Females were randomly assigned in equal numbers to receive injections of sesame oil (VEH) starting on day 12 (CONTROL), 1 mg of estradiol-17β in VEH starting on day 12 (E212), or 1 mg of estradiol-17β in VEH starting day 13 (E213). The injections were initiated at 0700 or 1900 (corresponding to the time of day they first exhibited estrus) and continued at 6-hour intervals for 48 hours, resulting in 8 mg of estradiol-17β given in eight injections. Pregnant females were killed on day 112 of gestation and ovulation rate, litter size, implantation site length, fetal weight, crown-rump length, placental weight, and placental surface area were quantified. There were no differences among E212, E213, and CONTROL females in ovulation rate or litter size, which averaged 16.3 ± .7 and 11.8 ± .7, respectively. Fetal weight and crown-rump length were not different (P\u3e.10) among E212, E213, and CONTROL females, averaging 802 ± 26 g and 24.3 ± .3 cm. Placentae were markedly heavier (176 ± 14 and 174 ± 16 g vs. 134 ± 10 g,

Blood Flow to the Uterus

Pattern of blood flow to the bovine uterus was determined by using electromagnetic blood flow probes during the estrous cycle and early pregnancy to evaluate the effect of the early bovine conceptus on uterine blood supply. Pattern of blood flow through the middle uterine artery of pregnant and nonpregnant cows was similar until day 14 after mating or estrus. Between days 14 and 18 of pregnancy, blood flow to the uterine horn containing the conceptus increased two-to-threefold, whereas blood flow to the other uterine horn in these cows remained constant. By day 19 of pregnancy, blood to the pregnant horn had returned to the level on day 13. Blood flow to both uterine horns of pregnant cows was low from days 19 to 25 and then increased to the pregnant horn through the remainder of pregnancy. Uterine blood flow during the estrous cycle of nonpregnant cows was positively associated with systemic concentrations of estradiol, whereas during pregnancy blood flow was positively related with progesterone concentration. These data indicate local control of uterine blood flow by the bovine conceptus, which may function to create optimal conditions for the continuation of pregnancy

Differential Prepartum and Postpartum Growth Patterns of Yorkshire and Meishan Piglets Gestated in the Same Uterine Environment

While Yorkshire fetal growth appears to depend on increasing placental size, more extensive vascularization of a smaller placenta appears to support Meishan fetal growth. Further studies are needed to extend our knowledge of the mechanisms controlling placental growth and vascularization. The ability to manipulate conceptus size may allow producers the opportunity to increase litter size in domestic pigs. More piglets farrowed per sow per year combined with the effects of fetal genotype on postpartum growth rate, as confirmed by the current study, would allow more efficient pork production

Selection for Litter Size by Using the Ratio of Piglet Weight: Placental Weight as a Measure of Placental Efficiency

The Chinese have been selectively breeding pigs for 7,000 to 10,000 years for increased numbers of pigs born, regardless of birth weight, indirectly resulting in the optimization of placental size and vascularity. In the United States, pig producers have generally selected for larger piglets at birth, resulting in a marked variation in placental size and vascularity. This tremendous variation in placental size and vascularity present within a litter may be ultimately limiting litter size. Therefore, by selecting against the large relatively avascular placentae, the potential for dramatically increasing litter size exists

The Effect of Uterine Environment on Meishan and Yorkshire Fetal Development and Placental Size and Vascularity

When Meishan (M) and Yorkshire (Y) embryos were cotransferred to Y recipients that were then allowed to farrow, it was observed that the birth weights of M and Y littermates were similar averaging 1.15 ± .06 kg. In contrast, placentae matched to M piglets were markedly smaller (.70% lighter) and more vascular (.two-fold) than Y placentae. To investigate the effect of uterine environment on conceptus development to term, M and Y embryos were cotransferred to M recipients (n=3) that were slaughtered one day before expected parturition (day 113). Fetal weight, placental weight, and placental surface area were recorded. Additionally, a section of the intact maternal placental interface was excised, fixed, embedded, sectioned, and stained to allow quantitation of the placental vascular density (PVD). As observed when M and Y fetuses were cogestated by Y recipients, littermate M and Y fetuses gestated in M uteri were similar in weight (1.04 ± .03 vs. 1.03 ± .05 kg) at term. Further, M conceptuses exhibited markedly reduced (P\u3c.03) placental weights (170 ± 19 vs. 249 ± 10 g) and surface areas (1017 ± 70 vs. 1506 ± 96 cm 2 ) compared with their Y littermates. As was the case for conceptuses gestated in Y uteri, the similarity in fetal weight between the two breeds with very different placental sizes appears to result from an increased (P\u3c.09) M PVD compared with littermate Y fetuses (2.5 ± .3 vs. 1.4 ± .4%). These data indicate that in both the M and Y uterine environment, the reduced size of the M compared with Y placenta is compensated for by an increase in PVD. Currently it is unknown whether M placentae contain a greater amount of vasculature (total volume) or a similar amount of vasculature simply squeezed into a smaller space. To investigate breed differences in total placental vasculature we have perfused placentae of M and Y conceptuses cogestated in M uteri on d 113 of gestation with vascular casting material and will compare the volumes of the corrosion casts

A Decreased Placental Size and Increased Vascular Density Results in Increased Prolificacy in the Meishan Pig

The Chinese Meishan pig farrows 3 to 5 more pigs per litter than U.S. pig breeds. When Meishan and Yorkshire embryos are co-transferred to a Yorkshire recipient, Meishan fetuses and placentae are smaller than Yorkshire fetuses and placentae through day 90 of gestation. At farrowing, Meishan placentae are still smaller than Yorkshire placentae; however, Meishan fetuses are born at the same weight as their Yorkshire littermates. This tremendous growth of the Meishan fetus between day 90 and term is the result of an increased vascularization of the Meishan placenta. In this experiment we investigated the time course of placental vascular development of Meishan and Yorkshire conceptuses during late gestation. Our results demonstrate that Yorkshire fetuses increase the potential for nutrient extraction from the maternal blood by increasing the size of their placentae; however, Meishan fetuses achieve the same end by increasing the density of placental blood vessels while maintaining a constant placental size. The increased vascular density of the Meishan placenta then allows the conceptus to occupy less space in the uterus, allowing more fetuses to survive to term

Selection of Piglets with a Reduced Placental Size Does Not Hinder Production Traits

Using a purebred population of Yorkshire (Y) females, our laboratory recently reported that the ratio of a piglet\u27s weight to that of its placenta (RATIO) varies ≈threefold within a litter. This variation in RATIO is due predominantly to variations in placental weight that are known to be a limiting factor in litter size. It was further determined that selection of boars and gilts with a higher than average RATIO for breeding resulted in an increased litter size and reduced placental weights. The objective of this experiment was to examine the effects of RATIO on economically important production traits (21- day weight, days to 105 kg and backfat and loin area at 105 kg) in a purebred breeding stock herd of Y and Landrace pigs. Sows were monitored throughout farrowing, and as each piglet appeared its umbilical cord was clamped close to the dam\u27s vulva and again near the neonates body then cut between the clamps. A number designating birth order was then tied around the exposed umbilical cord with surgical silk and the tagged umbilical cord was allowed to retract back into the birth canal. Each piglet was then notched to match its numbered placenta. Following expulsion, placentae were separated, piglets and placentae weighed, and RATIO determined for each. Piglets were individually weighed at 21 days and scanned by ultrasound at 105 kg for backfat thickness and loin area. Placental weight exhibited a significant (P\u3c.0001) negative correlation with RATIO (r=- .73), whereas birth weight did not (r=.09, P\u3e.25). Further, neither 21-day weight nor days to 105 kg were associated with RATIO. Additionally, carcass quality was not associated with RATIO. These data indicate that piglet selection based on a high RATIO (increased placental efficiency) is not detrimental to economically important production traits. Data will continue to be compiled on the tagged gilts as they reach breeding age to determine if their selection for increased placental efficiency results in increased litter size