169,815 research outputs found
A SHARP model of bid–ask spread forecasts
No full textThis paper proposes an accurate, parsimonious and fast-to-estimate forecasting model for integer-valued time series with long memory and seasonality. The modelling is achieved through an autoregressive Poisson process with a predictable stochastic intensity that is determined by two factors: a seasonal intraday pattern and a heterogeneous autoregressive component. We call the model SHARP, which is an acronym for seasonal heterogeneous autoregressive Poisson. We also present a mixed-data sampling extension of the model, which adopts the historical information flow more efficiently and provides the best (among all the models considered) forecasting performances, empirically, for the bid-ask spreads of NYSE equity stocks. We conclude by showing how bid-ask spread forecasts based on the SHARP model can be exploited in order to reduce the total cost incurred by a trader who is willing to buy or sell a given amount of an equity stock. (C) 2019 International Institute of Forecasters. Published by Elsevier B.V. All rights reserved
Assessing systemic risk due to fire sales spillover through maximum entropy network reconstruction
No full textMonitoring and assessing systemic risk in financial markets is of great importance but it often requires data that are unavailable or available at a very low frequency. For this reason, systemic risk assessment with partial information is potentially very useful for regulators and other stakeholders. In this paper we consider systemic risk due to fire sales spillovers and portfolio rebalancing by using the risk metrics defined by Greenwood et al. 2015). By using a method based on the constrained minimization of the Cross Entropy, we show that it is possible to assess aggregated and single bank's systemicness and vulnerability, using only the information on the size of each bank and the capitalization of each investment asset. We also compare our approach with an alternative widespread application of the Maximum Entropy principle allowing to derive graph probability distributions and generating scenarios and we use it to propose a statistical test for a change in banks' vulnerability to systemic events. (C) 2018 The Author(s). Published by Elsevier B.V
Compatibility of the bacterial entomopathogen Pseudomonas protegens with the natural predator Chrysoperla carnea (Neuroptera: Chrysopidae)
No full textThe susceptibility of the green lacewing Chrysoperla carnea to the soil-dwelling bacterial entomopathogen Pseudomonas protegens CHA0 was investigated in this study. Laboratory bioassays were conducted on larval instars exposed to different bacterial concentrations by both direct feeding and indirectly by offering a pre-treated insect prey. Potential toxicity was assessed through dose-response bioassays, while possible sublethal effects were evaluated on immature development time and the reproductive performance (fecundity) of adults emerging from treated juveniles. As a result, no significant effects were observed on larval survival and development in a comparison between treated and untreated (control) groups. No significant impact on adult emergence and no detrimental effects on female fecundity were detected. Everything considered, the use of P. protegens in the agroecosystem appears to be compatible with chrysopids
Localisation of type IV fibronectin and elastin in the flexor digitorum tendons and in the perichondrium during prenatal development of the human hand
No full textAN IMMUNOHISTOCHEMICAL STUDY EVIDENCES GHRELIN AND ITS RECEPTOR IN THE HAIR FOLLICLE OF THE SHEEP
No full textGhrelin is a peptide hormone discovered in 1999. It is mainly secreted by the endocrine
cells of the gastrointestinal tract and acts by binding to a specific receptor. Ghrelin
presents a wide tissue distribution and is involved in numerous central and peripheral
actions including hormonal, orexigenic, neurological, cardiovascular, and immunological
activities (1).In this work, the expression and localization of ghrelin and its receptor was
investigated in the skin of sheep by means of immunohistochemistry.
The immunohistochemical reaction was performed on ovine skin samples collected from
the neck ventral region of healthy animals regularly slaughtered at the abattoir. Samples
were fixed in formalin and embedded in paraffin. Dewaxed sections were incubated with
3% peroxidase-blocking solution and with normal goat serum to block the endogenous
peroxidase activity and non-specific binding respectively. Successively, serial sections
were incubated overnight with polyclonal anti-Ghrelin and anti-Ghrelin receptor
antibodies (Abcam Cambridge UK). The reaction was visualized using Vectastain ABC kit
and DAB (Vector Laboratories, Burlingame, CA, USA).
The analyses performed evidenced a clear and intense immunostaining for both ghrelin
and its receptor in the ovine skin. Staining was mainly localized in the hair follicles (HF).
Positivity to ghrelin was observed in a short area of the HF at the level of the soprabulbar
region; it involved the inner cells of the outer root sheath, including the companion layer,
and the cells of the inner root sheath. The receptor, instead, was observed in all cell
layers of the outer root sheath and extended more than ghrelin, from the soprabulbar
region to the isthmus. Other than HF, ghrelin showed a weak positivity in the soprabasal
layers of the epidermis which nevertheless were negative to the receptor. Finally, the
receptor was clearly expressed by the cells of the sweat glands.
At present, the skin is described as an endocrine organ since it is the target of several
endocrine signals and, at the same time, it is itself capable of producing substances with
hormone-like activity (2). The study of ghrelin and, more in general, of adipokines at the
skin level represent an interesting and current topic for domestic animals including
sheep. It was shown that some adipokines, such as leptin and adiponectin, are widely
involved in the metabolism of the skin, and, more specifically, of the HF in both
physiological and pathological conditions (3, 4). Ghrelin is a recently discovered molecule
and there are until now a few surveys on ghrelin at the skin level. However the strong
immunohistochemical expression of ghrelin and its receptor evidenced in the HF of the
sheep let us to suppose that ghrelin may have a role in the HF activity probably acting
through a paracrine or autocrine mechanism
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A Theoretical Model for the Extraction and Refinement of Natural Resources
No full textThe modelling of production in microeconomics has been the subject of heated debate. The controversial issues include the substitutability between production inputs, the role of time and the economic consequences of irreversibility in the production process. A case in point is the use of Cobb-Douglas type production functions. This approach completely ignores the physical process underlying the production of a good. We examine these issues in the context of the production of a basic commodity (such as copper or aluminium). We model the extraction and the refinement of a valuable substance which is mixed with waste material, in a way which is fully consistent with the physical constraints of the process. The resulting analytical description of production unambiguously reveals that perfect substitutability between production inputs fails if a corrected thermodynamic approach is used. We analyze the equilibrium pricing of a commodity extracted in an irreversible way. The thermodynamic model allows for the calculation of the ”energy yield” (energy return on energy invested) of production alongside a financial (real) return in a two-period investment decision. The two investment criteria correspond in our economy to a different choice of numeraire and means of payment and corresponding views of the value of energy resources. Under an energy numeraire, energy resources will naturally be used in a more parsimonious way
Ultrasonographic Kinetic of the carpal tunnel and its change during the carpal tunnel syndrome
No full textA new factor involved during childbirth labor: the importance of having a good dental occlusion
No full textIt is widely recognized that the physiology of childbirth labor largely depends on the interaction between three factors: a) the force generated by uterine contractions; b) the structure and characteristics of the birth canal and c) the fetus. Harmony between these three variables determines the initiation of maternal dynamic phenomena and the establishment of an optimal maternal-fetal balance in which both warrant for a correct delivery timing. The present study considered the above known factors and assessed if any other factor, still not recognized, could also play a role, and eventually modify the timing of delivery during the expulsive period. In particular, we focused our attention on the role played by the temporomandibular joint and dental occlusion on maternal body balance and on the stability of muscular reflected forces. The importance of assessing the temporomandibular function and the dental occlusion lies in the fact that any alteration in chewing or in temporomandibular joint (TMJ) mobility and occlusion brings to relevant modifications on the vertebral column and pelvic girdle. Our hypothesis is based on the evidence that those women who have any kind of alteration in their dental occlusion, can have an altered capability of pushing during the expulsive period, as the force applied on the pelvic floor is not expressed. Moreover, recent studies have highlighted a relationship between temporomandibular dysfunctions and sleep apnea syndrome and between sleep apnea syndromes and pregnancy. These relationships are explored in this study
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