117,603 research outputs found
Testing the exogeneity assumption in panel data models with "non classical" disturbances
No full textThis paper is concerned with the use of the Durbin-Wu-Hausman test for correlated effects with panel data. The assumptions underlying the construction of the statistic are too strong in many empirical cases. The consequences of deviations from the basic assumptions are investigated. The size distortion is assessed. In the case of measurement error, the Hausman test is found to be a test of the difference in asymptotic biases of between and within group estimators. However, its 'size' is sensitive to the relative magnitude of the intra-group and inter-group variations of the covariates, and can be so large as to preclude the use of the statistic in this case. We show to what extent some assumptions can be relaxed in a panel data context and we discuss an alternative robust formulation of the test. Power considerations are presented
Forces on a spherical conducting particle in E x B fields
No full textThe forces acting on a spherical conducting particle in a transversely flowing magnetized plasma are calculated in the entire range of magnetization and Debye length, using the particle code SCEPTIC3D (Patacchini and Hutchinson 2010 Plasma Phys. Control. Fusion 52 035005, 2011 Plasma Phys. Control. Fusion 53 025005). In short Debye length (i.e. high density) plasmas, both the ion-drag and Lorentz force arising from currents circulating inside the dust show strong components antiparallel to the convective electric field, suggesting that a free dust particle should gyrate faster than what predicted by its Larmor frequency. In intermediate to large Debye length conditions, by a downstream depletion effect already reported in unmagnetized strongly collisional regimes, the ion-drag in the direction of transverse flow can become negative. The internal Lorentz force, however, remains in the flow direction, and large enough in magnitude so that no spontaneous dust motion should occur.National Science Foundation (U.S.)United States. Dept. of Energy (grant DE-FG02-06ER54891
ROSE-L and Sentinel-1 soil moisture retrieval: a simulated study
No full textIn the frame of the Copernicus Expansion Program, it is foreseen the launch of two L-band SAR satellites flying in constellation with Sentinel-1. This will offer an unprecedent opportunity of collecting data at L-band and C-band in a systematic and coordinated way. This study focuses on soil moisture retrieval applications and investigates the performances of a dual frequency multiplatform retrieval approach based on a simulated study. The objective is to assess the pros and cons of a coincident acquisition of C and L-band data, which is expected to improve the retrieval accuracy, with respect to an alternate acquisition of the two platforms that, on the contrary, would drastically reduce the revisit time of the System of Systems from 6 to 3 days or less. It was found that, if a multitemporal retrieval approach is exploited, the alternate acquisitions can provide retrieval accuracy better than individual acquisitions at each frequency, and close to that of coincident acquisitions, while keeping a much better temporal resolution of the soil moisture products
Geography and economic performance: exploratory spatial data analysis for Great Britain
No full textThis paper uses the techniques of exploratory spatial data analysis to analyse patterns of spatial association for different indicators of economic performance, and in so doing identify and describe the spatial structure of economic performance for Great Britain. This approach enables us to identify a number of significant local regimes – clusters of areas in which income per worker differs significantly from the global average – and investigate whether these come about primarily through spatial association in occupational composition or in productivity. Our results show that the contributions of occupational composition and productivity vary significantly across local regimes. The ‘winner’s circle’ of areas in the south and east of England benefits from both above average levels of productivity and better than average occupational composition, while the low income regime in the north of England suffers particularly from poor occupational composition
Involvement of endogenous tachykinins and CGRP in the motor responses produced by capsaicin in the guinea-pig common bile duct
No full textIn functional experiments, we have investigated the effect exerted by neurotransmitters released from capsaicin-sensitive primary afferent nerve terminals in the isolated guinea-pig common bile duct. In resting preparations, capsaicin (0.1 μM) produced a quick contraction (45.1±4% of KCl 80 mM) which was abolished by either atropine (1 μM) or tetrodotoxin (0.5 μM). The tachykinin receptor-selective antagonists GR 82334 (NK1 receptor-selective; 3 μM), MEN 11420 (NK2 receptor-selective; 1 μM) and sR 142801 (NK3 receptor-selective; 0.1 μM) administered separately failed to reduce the capsaicin-evoked contraction, whereas any combination of the three antagonists was effective: GR 82334 plus MEN 11420, 36±7% reduction; GR 82334 plus SR 142801, 48±4% reduction; MEN 11420 plus SR 142801, 55±3% reduction; GR 82334 plus MEN 11420 plus SR 142801, 57±5% reduction. Neither the CGRP1 receptor antagonist h-CGRP (8-37) (1.5 μM) nor the P(2x) purinoceptor antagonist PPADS (50 μM) affected the contractile response to capsaicin. The effect of capsaicin (0.1 μM) was abolished by pretreatment with capsaicin itself (10 μM for 15 min). Human calcitonin gene-related peptide (h-CGRP; 0.1 μM) mimicked the effect of capsaicin on resting preparations (contractile response =28% of KCl 80 mM). In preparations precontracted with a submaximal concentration of KCl (24 mM), and in the presence of atropine (1 μM), GR 82334 (3 μM) and MEN 11420 (3 μM), capsaicin (1 μM) produced a tetrodotoxin-insensitive long-lasting relaxation (45±3% reduction of tone, at 4 min from administration), which was unaffected by the nitric oxide (NO) synthase inhibitor, L-NOARG (100μM). h- CGRP (10-50 nM) produced a similar sustained relaxation of precontracted preparations (59±4% reduction of tone). h-CGRP (8-37) (1.5 μM) almost completely reversed file relaxations produced by both capsaicin and h-CGRP. Application of electrical field stimulation (EFS: trains of stimuli of 10 Hz; 0.25 ms pulse width; supramaximal voltage; for 60 s) to precontracted preparations produced a sustained, tetrodotoxin (1 μM)-sensitive relaxation (32±4% reduction of tone). L-NOARG (100 μM) greatly reduced (69±5% inhibition) the EFS-elicited relaxation. A complete reversal of the relaxant response to EFS into a contraction was obtained by administering L-NOARG to preparations in which a functional blockade of capsaicin-sensitive primary afferent neurons had been achieved by incubating the tissue with capsaicin (10 μM) for 15 min. At immunohistochemistry, tachykinin- and CGRP- immunoreactivities (TK-IR/CGRP-IR) were detected in varicose nerve fibers throughout the common bile duct, while TK-IR cell bodies were observed in the terminal portion (ampulla) only. In vivo pretreatment with capsaicin (50 mg/kg; 6-7 days before) decreased the number of CGRP-IR nerves, whereas the TK-IR neural network was apparently unchanged. In conclusion, our data provide functional evidence for the presence of capsaicin-sensitive primary afferent nerve endings in the guinea-pig terminal biliary tract, whose stimulation by capsaicin or EFS produces the release of tachykinins and CGRP. In addition, morphological evidence is provided that the bulk of TK-IR material in the biliary tract is contained in intrinsic neuronal elements, while CGRP in this tissue is of extrinsic origin only. Tachykinins, probably released in small amounts by capsaicin, act by activating receptors of the NK1, NK2 and NK3 type, most probably located on intrinsic cholinergic neurons, which in turn release ACh to produce the final excitatory motor response. The contractile response to capsaicin obtained in the presence of the three tachykinin receptor antagonists could be due to the co-released CGRP and/or to other unknown neurotransmitters. CGRP produces either indirect excitatory or direct inhibitory responses by stimulation of CGRP2 and CGRP1 receptors, respectively
Flowing plasmas and absorbing objects: analytic and numerical solutions culminating 80 years of ion-collection theory
No full textRecent computational and theoretical progress in understanding and calculating ion collection by negatively charged absorbing objects in a flowing plasma is outlined. The results are placed in the context of key theoretical achievements of prior research. Despite the topic's long history, and past profound insights, fully rigorous quantitative solution of the non-linear, multidimensional, self-consistent, kinetic-theory problem has not until recently been feasible. Now we are able to establish the adequacy or inadequacy of approximate treatments, and provide critical quantitative results. In the process, some qualitative surprises have also emerged
Evidence that tachykinins are the main NANC excitatory neurotransmitters in the guinea-pig common bile duct
No full text1. Application of electrical field stimulation (EFS; trains of 10 Hz, 0.25 ms pulse width, supramaximal voltage for 60 s) to the guinea-pig isolated common bile duct pretreated with atropine (1 μM), produced a slowly-developing contraction ('on' response) followed by a quick phasic 'off' contraction ('off peak' response) and a tonic response ('off late' response), averaging 16 ± 2, 73 ± 3 and 20 ± 4% of the maximal contraction to KCl (80 mM), n = 20 each, respectively. Tetrodotoxin (1 μM; 15 min before) abolished the overall response to EFS (n = 8). 2. Neither in vitro capsaicin pretreatment (10 μM for 15 min), nor guanethidine (3 μM, 60 min before) affected the excitatory response to EFS (n = 5 each), showing that neither primary sensory neurons, nor sympathetic nerves were involved. N(ω)-nitro-L-arginine (L-NOARG, 100 μM, 60 min before) or naloxone (10 μM, 30 min before) significantly enhanced the 'on' response (294 ± 56 and 205 ± 25% increase, respectively; n = 6-8, P < 0.01) to EFS. The combined administration of L-NOARG and naloxone produced additive enhancing effects (655 ± 90% increase of the 'on' component, n = 6, P < 0.05). 3. The tachykinin NK2 receptor-selective antagonist MEN 11420 (1 μM) almost abolished both the 'on' and 'off late' responses (P < 0.01; n = 5 each) to EFS, and reduced the 'off-peak' contraction by 55 ± 8% (n = 5, P < 0.01). The subsequent administration of the tachykinin NK1 receptor-selective antagonist GR 82334 (1 μM) and of the tachykinin NK3 receptor-selective antagonist SR 142801 (30 nM), in the presence of MEN 11420 (1 μM) did not produce any further inhibition of the response to EFS (P > 0.05; n = 5 each). At 3 μM, GR 82334 significantly reduced (by 68 ± 9%, P < 0.05, n = 6) the 'on' response to EFS. 4. The contractile 'off peak' response to EFS observed in the presence of both MEN 11420 and GR 82334 (3 μM each) was abolished (P < 0.01; n = 6) by the administration of the P2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 30 μM). PPADS (30 μM) selectively blocked (75 ± 9 and 50 ± 7% inhibition, n = 4 each) the contractile responses produced by 100 and 300 μM ATP. 5. Tachykinin-containing nerve fibres were detected by using immunohistochemical techniques in all parts of the bile duct, being distributed to the muscle layer and lamina propria of mucosa. In the terminal part of the duct (ampulla) some labelled ganglion cells were observed. 6. In conclusion, this study shows that in the guinea-pig terminal biliary tract tachykinins, released from intrinsic neuronal elements, are the main NANC excitatory neurotransmitters, which act by stimulating tachykinin NK2 (and possibly NK1) receptors. ATP is also involved as excitatory neurotransmitter. Nitric oxide and opioids act as inhibitory mediators/modulators in this preparation
Social Networks and Parental Behavior in the Intergenerational Transmission of Religion
No full textWe analyze the intergenerational transmission of the strength of religion focusing on the interplay between family and peer effects. We develop a theoretical model suggesting that both peer quality and parental effort are of importance for the religious behavior of the children. We then bring the model to the data by using a very detailed dataset of adolescent friendship networks in the United States. We find that, for religious parents, the higher is the fraction of religious peers, the more parents put effort in transmitting their religiosity, indicating cultural complementarity. For non-religious parents, we obtain the reverse, indicating cultural substitutability. Concerning the success in transmitting the religious trait, we find that, for religious parents, the fraction of religious peers has only an indirect effect (through parental effort) while, for non-religious parents, there is a lower indirect effect and a statistically significant and sizeable direct effect of peers on the transmission of the non-religious trait.religion, cultural transmission, peer effects, network fixed effects
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
Evidence that tachykinins are the main NANC excitatory neurotransmitters in the guinea-pig common bile duct.
No full text1. Application of electrical field stimulation (EFS; trains of 10 Hz, 0.25 ms pulse width, supramaximal voltage for 60 s) to the guinea-pig isolated common bile duct pretreated with atropine (1 μM), produced a slowly-developing contraction ('on' response) followed by a quick phasic 'off' contraction ('off peak' response) and a tonic response ('off late' response), averaging 16 ± 2, 73 ± 3 and 20 ± 4% of the maximal contraction to KCl (80 mM), n = 20 each, respectively. Tetrodotoxin (1 μM; 15 min before) abolished the overall response to EFS (n = 8). 2. Neither in vitro capsaicin pretreatment (10 μM for 15 min), nor guanethidine (3 μM, 60 min before) affected the excitatory response to EFS (n = 5 each), showing that neither primary sensory neurons, nor sympathetic nerves were involved. N(ω)-nitro-L-arginine (L-NOARG, 100 μM, 60 min before) or naloxone (10 μM, 30 min before) significantly enhanced the 'on' response (294 ± 56 and 205 ± 25% increase, respectively; n = 6-8, P 0.05; n = 5 each). At 3 μM, GR 82334 significantly reduced (by 68 ± 9%, P < 0.05, n = 6) the 'on' response to EFS. 4. The contractile 'off peak' response to EFS observed in the presence of both MEN 11420 and GR 82334 (3 μM each) was abolished (P < 0.01; n = 6) by the administration of the P2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 30 μM). PPADS (30 μM) selectively blocked (75 ± 9 and 50 ± 7% inhibition, n = 4 each) the contractile responses produced by 100 and 300 μM ATP. 5. Tachykinin-containing nerve fibres were detected by using immunohistochemical techniques in all parts of the bile duct, being distributed to the muscle layer and lamina propria of mucosa. In the terminal part of the duct (ampulla) some labelled ganglion cells were observed. 6. In conclusion, this study shows that in the guinea-pig terminal biliary tract tachykinins, released from intrinsic neuronal elements, are the main NANC excitatory neurotransmitters, which act by stimulating tachykinin NK2 (and possibly NK1) receptors. ATP is also involved as excitatory neurotransmitter. Nitric oxide and opioids act as inhibitory mediators/modulators in this preparation
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