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1.
In the rat the exact role of vagal fibers and the interaction between the extrinsic and intrinsic neural system in distention-induced gastrin release are still a matter of debate. Accordingly, the aim of the present study was to examine the contribution of afferent and efferent vagal fibers as well as intrinsic neurons on gastrin response to gastric distention. In anesthetized rats graded gastric distention by 5, 10 and 15 ml saline for 20 min caused a significant volume-dependent increase of plasma gastrin levels by 12+/-6 pg/ml (5 ml saline, n = 8, P =0.05), 26+/-7 pg/ml (10 ml saline, n = 10, P < 0.05) and 37+/-7 pg/ml (15 ml saline, n = 8, P < 0.01 ), respectively. To examine the role of the extrinsic vagal innervation, gastrin response to distention was studied in anesthetized rats after bilateral truncal vagotomy (n = 9) or selective afferent vagotomy following pretreatment with capsaicin (n = 6). Stimulation of gastrin release by 10 ml distention in sham-operated control rats was reversed to an inhibition after truncal vagotomy (26+/-7 vs. -11+/-4 pg/ml; P<0.05) and capsaicin-treatment (37+/-18 vs. -34+/-11 pg/ml; P<0.05). A contribution of cholinergic mechanisms to this vagovagal-mediated stimulation of distention-induced gastrin release was excluded, since atropine (100 microg/kg/h; n = 8) further augmented distention-stimulated gastrin release. Since bombesin/gastrin-releasing peptide (GRP)-neurons contribute to vagally stimulated gastrin secretion, we have examined gastrin response to distention in the presence of the specific bombesin-receptor antagonist D-Phe6-BN(6-13)OMe (400 microg/kg/h: n = 10). This bombesin-antagonist completely reduced distention-stimulated gastrin release in vivo. In contrast, distention of the isolated, extrinsically denervated stomach significantly decreased gastrin release by 13+/-5 pg/min (5 ml saline, n = 8, P < 0.05), 28+/-8 pg/min (10 ml saline, n = 11, P < 0.05) and 35+/-10 pg/min (15 ml saline, n = 8, P < 0.01), respectively, without changing the activity of bombesin/GRP-neurons. Distention-induced decrease of gastrin release was attenuated to 50 percent by atropine (10(-7) M: n = 10) or tetrodotoxin (TTX) (10(-6) M; n = 10), respectively. These data demonstrate, that in anesthetized rats distention-stimulated gastrin secretion depends on the activation of a vagovagal reflex and intrinsic bombesin/GRP-neurons. In contrast distention of the isolated rat stomach inhibits gastrin release in part via intrinsic cholinergic pathways and other as yet unknown mechanisms. 相似文献
2.
Journal of Materials Science Letters - 相似文献
3.
This paper analyses the potential roles of computerized systems in supporting the decision-making process. Toward this end, we propose an expository process model of decision-making and develop a framework that provides the infrastructure for the analysis. The proposed process model draws on two well-known models in the literature and enumerates eight distinct phases in decision-making. The framework developed is based on an integration of this process model with Simon's notion of 'decision-structuredness'. Unlike any of the existing frameworks, the suggested framework permits a micro-level analysis of support system roles. The analysis is intended as a pre-design guide, to help systems developers and users to identify support potential and possibilities, and to target their activities accordingly. 相似文献
4.
Other than temperature and voltage, load plays a key role in anodic bonding process. In this paper we present a new design of top electrode (cathode) for anodic bonding machine by which the bonding time has been reduced up to 30 % in case of bare silicon wafer at ?400 V and approximate 52 % in case of oxidized silicon wafer with Pyrex glass bonding at ?800 V. Experimentally it has been observed there was no bonding in oxidized silicon wafer with Pyrex glass up to ?600 V by using standard design while it has been successfully bonded at same voltage (?600 V) by using new design. 相似文献
5.
Composites based on natural rubber (NR) and containing organophilic and pristine layered silicates of natural and synthetic origin were produced by melt compounding and sulfur curing. The curing, thermomechanical, and mechanical properties of the mixes, which contained 10 phr (parts per hundred parts of rubber) silicates, were determined. The dispersion of the silicates was studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Organophilic clays accelerated the sulfur curing of NR, which was believed to occur because of a complexation reaction in which the amine groups of the clay intercalants participated. The property improvements caused by the fillers were ranked as follows: organophilic clays > pristine synthetic layered silicate (sodium fluorohectorite) > pristine natural clay (purified sodium bentonite) > precipitated nonlayered silica (used as a reference). This was attributed to partial intercalation of the organophilic clay by NR on the basis of XRD and TEM results and to the high aspect ratio of the fluorohectorite. Apart from intercalation, severe confinement (i.e., the collapse of the interlayer distance) of the organoclays was observed. This peculiar feature was traced to the formation of a zinc coordination complex, which extracted the amine intercalant of the organoclays, thus causing the collapse of the layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 813–819, 2004 相似文献
6.
Deepthi N. Ratnayake Hassan B. Kazemian Syed A. Yusuf 《Neural computing & applications》2014,25(1):1-14
Any sniffer can see the information sent through unprotected ‘probe request messages’ and ‘probe response messages’ in wireless local area networks (WLAN). A station (STA) can send probe requests to trigger probe responses by simply spoofing a genuine media access control (MAC) address to deceive access point (AP) controlled access list. Adversaries exploit these weaknesses to flood APs with probe requests, which can generate a denial of service (DoS) to genuine STAs. The research examines traffic of a WLAN using supervised feed-forward neural network classifier to identify genuine frames from rogue frames. The novel feature of this approach is to capture the genuine user and attacker training data separately and label them prior to training without network administrator’s intervention. The model’s performance is validated using self-consistency and fivefold cross-validation tests. The simulation is comprehensive and takes into account the real-world environment. The results show that this approach detects probe request attacks extremely well. This solution also detects an attack during an early stage of the communication, so that it can prevent any other attacks when an adversary contemplates to start breaking into the network. 相似文献
7.
Thermoplastic elastomers, prepared by melt blending of natural rubber (NR) and isotactic polypropylene (PP) through a dynamic vulcanization technique, were developed during the later 1970s. However, they have certain drawbacks due to thermal degradation and higher molecular weight of NR. In the study reported here, NR was masticated to different levels prior its addition to isotactic polypropylene to improve the flow properties and to reduce the incompatibility resulting from molecular weight mismatch of NR/PP thermoplastic blends. Mixing energy curves of uncrosslinked blends and those of dynamically vulcanized blends crosslinked using different cure systems were compared. The mixing energy curves of blends containing NR of different molecular weight (M n) and two grades of PP (injection and film grades) were also compared. Technological and processing properties of the dynamically vulcanized (sulphur and peroxide cure systems) and unvulcanized blends were compared with those of the samples containing unmasticated NR. The results indicated that a number average molecular weight in the range 4 × 105 for NR increased the procoessability without significantly affecting the technological properties of NR/PP thermoplastic blends. Among the three cure systems studied Luperox 101 and dicumyl peroxide gave better technological properties than the sulphur‐cured samples. Two antioxidants, viz. quinoline (TDQ) and imidazole (MBI) type, were tried in NR/PP blends. It was found that TDQ imparts better aging resistance compared to MBI. The improvement in processability due to the reduction in molecular weight of natural rubber by mastication is more noticeable in the case of peroxide vulcanized blends compared to sulphur vulcanized samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2063–2068, 2004 相似文献
8.
Suseela Sreelekshmi Philomina Joseph Rani Varghese Chakkalakkal M. Preethy Sivasankaran Bijoy Nandan 《Lakes & Reservoirs: Research and Management》2020,25(2):143-156
We estimated the tree structural variables (density, frequency and basal area) of true mangroves and soil variables like particle size distribution, carbon, available nitrogen and phosphorus, sulphur, nutrient cations (K, Na, Ca, Mg) of Cochin mangroves and examined the relationship between vegetation and environment. The study sites were classified as seaward fringe, riverine and interior. Of the thirteen true mangrove species present, Avicennia officinalis, Sonneratia caseolaris and Excoecaria agallocha showed higher Importance Value Index. The mean stem density varied from 80 to 25,000 no./ha and basal area from 0.1 to 39.68 m2/ha. Seaward mangroves showed maximum stand basal area and biomass production while riverine exhibited maximum density. Maturity Index value of Cochin mangroves revealed a very low degree of structural maturity. Interior mangroves were characterized by silty soil with higher nutrient concentrations. Principal component analysis of soil data revealed that the major factors influencing mangrove vegetation were soil texture, nutrients, salinity and oxidation–reduction potential. The stem density and basal area of different species correlated highly with soil nutrients and texture (p < .001) while salinity showed negative correlations with vegetation characteristics. The data generated in the study would be fundamental in site‐specific management and conservation efforts of these degrading mangroves. 相似文献
9.
Harish C. Barshilia N. Selvakumar B. Deepthi K.S. Rajam 《Surface & coatings technology》2006,201(6):2193-2201
Approximately 1.5 μm thick CrN and CrAlN coatings were deposited on silicon and mild steel substrates by reactive direct current (DC) magnetron sputtering. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the coatings was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD data showed that the CrN and CrAlN coatings exhibited B1 NaCl structure. Nanoindentation measurements showed that as-deposited CrN and CrAlN coatings exhibited a hardness of 18 and 33 GPa, respectively. Results of the surface analysis of the as-deposited coatings using SEM and AFM showed a more compact and dense microstructure for CrAlN coatings. The thermal stability of the coatings was studied by heating the coatings in air from 400 to 900 °C. The structural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data revealed that CrN coatings got oxidized at 600 °C, whereas in the case of CrAlN coatings, no detectable oxides were formed even at 800 °C. After annealing up to 700 °C, the CrN coatings displayed a hardness of only about 7.5 GPa as compared to CrAlN coatings, which exhibited hardness as high as 22.5 GPa. The potentiodynamic polarization measurements in 3.5% NaCl solution indicated that the CrAlN coatings exhibited superior corrosion resistance as compared to CrN coatings. 相似文献
10.
S. Shanmuga Priya D. Yuvaraj T. Satyanarayana Murthy Varghese S. Chooralil S. Navaneetha Krishnan P. Banumathy P. SundaraVadivel 《计算机系统科学与工程》2022,43(3):887-896
Authentication is important to the security of user data in a mobile cloud environment. Because of the server’s user credentials, it is subject to attacks. To maintain data authentication, a novel authentication mechanism is proposed. It consists of three independent phases: Registration, login, and authentication and key agreement. The user registers with the Registration Center (RC) by producing a secret number that isn’t stored in the phone, which protects against privileged insider attacks. The user and server generate a nonce for dynamic user identity and agree on a session secret key for safe communication. The passwords are not stored on the computer or provided in plain text, they are resistant to replay, guessing, and stolen verification attacks. The suggested protocol uses a one-way hash function and XOR operations, with the client having remote access to a large number of servers over a secure communication channel. Concentrates on HMAC and SHA3 for Collision Free Hashing and to overcome length extension attacks. HMACs are substantially less affected by collisions than their underlying hashing algorithms alone. So adding an HMAC to an MD5 or SHA hash would make it substantially more difficult to break via a rainbow table. 相似文献