IMPACTS OF TRADES IN AN ERROR-CORRECTION MODEL OF QUOTE PRICES

In this paper we analyze and interpret the quote price dynamics of 100 NYSE stocks with varying average trade frequencies. We specify an error-correction model for the log difference of the bid and the ask price, with the spread acting as the error-correction term, and include as regressors the characteristics of the trades occurring between quote observations, if any. We find that short duration and medium volume trades have the largest impacts on quote prices for all one hundred stocks, and that buyer initiated trades primarily move the ask price while seller initiated trades primarily move the bid price. Trades have a greater impact on quotes in both the short and the long run for the infrequently traded stocks than for the more actively traded stocks. Finally, we find strong evidence that the spread is mean reverting

Low Frequency Fatigue in Human Quadriceps is Fatigue Dependent and Not Task Dependent

It is well accepted that a low intensity/long duration isometric contraction induces more low frequency fatigue (LFF) compared to a high-intensity/short-duration contraction. However, previous reports examined the intensity/duration of the contraction but did not control the level of fatigue when concluding fatigue is task dependent. The purpose of this study was to determine whether a long duration/low intensity fatiguing contraction would induce greater LFF than a short duration/high-intensity contraction when the quadriceps muscle was fatigued to similar levels. Eighteen healthy male subjects performed quadriceps contractions sustained at 35% and 65% of maximal voluntary contraction (MVC) on separate days, until the tasks induced a similar amount of fatigue (force generating capacity = 45% MVC). Double pulse torque to single pulse torque ratio (D/S ratio) was obtained before, immediately and 5 min after fatigue along with the electromyographic (EMG) signal from vastus medialis (VM) and rectus femoris (RF). The D/S ratio significantly (p \u3c 0.05) increased by 8.7 ± 8.5% (mean ± SD) and 10.2 ± 9.2% after 35% and 65% tasks, respectively, and remained elevated 5 min into recovery; however, there was no significant difference in ratio between the two sessions immediately or 5 min post-fatigue (p \u3e 0.05) even though the endurance time for the 35% fatigue task (124 ± 39.68 s) was significantly longer (p = 0.05) than that of the 65% task (63 ± 17.73 s). EMG amplitude and median power frequency (MPF) analysis also did not reveal any significant differences between these two sessions after fatigue. These findings indicate that LFF fatigue is fatigue dependent as well as task intensity/duration dependent. These findings assist us in understanding task dependency and muscle fatigue

A Cross-Taxonomic Comparison of Insect Responses to Grassland Management and Land-Use Legacies

Many species of plants and animals associated with grasslands are rare or declining due to habitat loss and degradation. Although grassland plants and insects evolved in the context of both grazing and fire, the appropriate use of grazing and fire has been debated among those concerned with protecting insect communities. We established an experiment to test insect responses to three grassland management treatments: (1) patch-burn graze (burning of spatially distinct patches and free access by cattle), (2) grazeand- burn (burning of entire tract with free access by cattle), and (3) burn-only. Because we expected that land-use legacies could also affect insect abundance and diversity, we evaluated effects of time since fire, grazing history, remnant history (remnant or reconstructed grassland) and pre-treatment vegetation characteristics, which were assumed to be a legacy of prior land-use. Butterflies (Lepidoptera), ants (Hymenoptera: Formicidae), and leaf beetles (Coleoptera: Chrysomelidae) were surveyed for three years to compare their responses to each of these treatments as measured by abundance, richness and species diversity. Each of these taxa is relatively diverse and was expected to have the potential to have strong negative responses to grazing and burning, but we predicted more positive responses to patch-burn grazing. Our results showed that land-use legacies affected insect abundance, richness and diversity, but treatments did not. Ant abundance was lower in tracts with a history of heavy grazing. Ant species richness was positively associated with pre-treatment time since fire and vegetation height and negatively associated with pre-treatment proportion native plant cover. Butterfly abundance was positively associated with pre-treatment litter cover. Leaf beetle diversity was positively associated with pre-treatment native plant cover, and leaf beetle abundance was negatively associated with time since fire. Our results indicate that land-use legacies can exert more influence on grassland insect community composition than current management, but the particular aspects of these land-use legacies that are important vary across insect taxa. The implications of these finding are that (1) land-use legacies should garner more attention in grassland management and (2) conservation of grassland insect communities will be improved by taxonspecific analysis of land-use legacy variables

Thrombopoietin: A Novel Bone Healing Agent

poster abstractCritical-size defects in bones do not heal spontaneously and usually require the use of grafts. Unfortunately, grafts have several limitations. To improve bone formation, many clinicians now use bone morphogenetic proteins (BMP), particularly in spinal fusion, fracture healing, and in critical-size defect regeneration. However, multiple side effects of BMP treatment have been uncovered including increased incidence of cancer. Thus, there is great interest in alternatives that allow for safe and effective bone regeneration. Here we show the ability of thrombopoietin (TPO), the main megakaryocyte growth factor, to heal critical-size femoral defects rodents. 5mm or 4mm segmental defects were created in the femur of Long Evans rats or C57BL/6 mice, respectively. The defects were filled with a novel bioabsorbable scaffold which was loaded with recombinant human TPO, BMP-2, or saline, and held stable by a retrograde 1.6 mm intramedullary Kirschner wire (rats) or 23G needle (mice). Xrays were taken every 3 weeks in rats and weekly in mice. Animal were sacrificed at 15 weeks, at which time micro-computed tomography (μCT) and histological analyses were performed. The results observed in mice and rats were similar. The saline control group did not show bridging callus at any time. Both the BMP-2 and TPO groups healed the defect, although bridging callus was evident at earlier times in the BMP-2 groups. However, the TPO groups showed a much more remodeled and physiologic contour on both Xray and μCT. μCT and histological analysis confirms that compared to BMP-2, TPO-treated specimens have a thicker cortex but smaller diameter and smoother contour. TPO appears to restore the original bone contour by stimulating osteoblastogenesis, allowing for periosteal bridging and stabilization to occur, while simultaneously stimulating osteoclast formation. Thus, TPO may serve as a novel bone healing agent

Megakaryocytes: Regulators of Bone Mass and Hematopoiesis

poster abstractEmerging evidence demonstrates that megakaryocytes (MK) play a key role in regulating skeletal homeostasis and hematopoiesis. Recent reports show that MK reside in close proximity to hematopoietic stem cells (HSC). Genetic depletion of MK resulted in mitotic activation of HSC suggesting that MK maintain HSC quiescence. Other studies demonstrated that following irradiation, surviving MK migrate to endosteal surfaces where osteoblast (OB) lineage cells dramatically increase and promote engraftment of transplanted HSC. Here we investigated if MK directly impact hematopoiesis or whether they indirectly support HSC function through their interaction with OB-lineage cells. Our data suggests that LSK (Lin-Sca+CD117+, an enriched HSC population) co-cultured with MK and OB generate significantly higher numbers of colony forming cells (HSC function) compared to LSK cocultured with either MK or OB alone. The functionality of this in vitro data was confirmed in vivo with transplantation studies which showed increased engraftment in mice transplanted with LSK cells co-cultured with OB and MK compared to LSK cells co-cultured with OB alone. To test if loss of MK negatively impacts osteoblastogenesis, we generated conditional knockout mice where cMpl, the receptor for the main MK growth factor, thrombopoietin (TPO), was deleted in MK (cMplfl/fl x PF4Cre). Unexpectedly, these mice exhibited a 10-fold increase in platelet numbers, megakaryocytosis, a dramatic expansion of phenotypically defined hematopoietic precursors, and a remarkable 20-fold increase in the bone volume fraction. Collectively, these data indicate that while MK modulate HSC function, this activity is in part mediated through interactions with OB and suggest a complex role for TPO and MK in HSC regulation. While work is needed to further elucidate mechanisms, understanding the coordinated interaction between MK, OB, HSC, and TPO/Mpl should inform the development of novel treatments to enhance HSC recovery following myelosuppressive injuries, as well as bone loss diseases, such as osteoporosis