bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum Fatigue Crack Resistance
Authors: Throop JF , Miller GA
Published: March 2009

An evaluation is made of the influence of mechanical properties on fatigue crack growth rate. Data representing SAE 4340 and modified 4330 steels show that for levels of the stress intensity factor, K, below about 40 ksi√in. mechanical properties have little influence on growth rate. However, at higher K levels both the product of Young's modulus, yield strength, and fracture toughness and the product of Young's modulus, tensile strength, and true strain at fracture seem to be reasonable indexes of crack growth resistance. For K levels above 40 ksi√in. the fatigue crack growth rate is minimized by tempering 4340 and modified 4330 steel at temperatures of about 1000 and 1100 F, respectively.
The Role of Residual Stresses in Increasing Long-life Fatigue Strength of Notched Machine Members
Authors: Nelson DV , Ricklefs RE , Evans WP
Published: March 2009

High compressive residual stress and high hardness were utilized to obtain high fatigue strength in nonrotating bending. A compressive residual stress of 250 ksi, obtained in a 0.25-in. notch in SAE 1045 specimens of 1.50-in. diameter, resulted in a one million-cycle fatigue strength of ±230 ksi. An investigation showed that, over the range studied, maximum residual stress from heat treatment was produced with maximum hardness, medium carbon content, maximum section size (to 4-in. diameter), and minimum hardenability. At high hardness, cold working by shot peening was found to decrease the high residual stress from heat treatment. Fatigue tests were run on peened and unpeened specimens of various hardnesses with a machine that had provisions for applying a mechanical mean stress. Various net mean stress conditions, residual plus mechanical, could then be obtained. The fatigue strength of hard specimens with a tensile, applied mean stress was reduced by the presence of crack-like defects created by peening. Data were interpreted in terms of a theory in the literature involving crack initiation, crack propagation, and yielding.
Metal Fatique with Elevated Temperature Rest Periods
Authors: Sandor BI
Published: March 2009

Intermittent annealing of oxygen-free high-conductivity copper is used to investigate the accumulation of low-cycle fatigue damage under total diametral strain control. Cyclic strain-induced cold work can be removed independently of the number of prior strain cycles or annealing periods. Specimens with frequent intermittent annealing have slightly extended fatigue lives instead of reductions in life predicted on the basis of the Manson-Coffin relation.

Frequent rest periods at mildly elevated temperature reduce the cyclic plastic strain and retard the fatigue damage process in mild steel tested under axial stress control. Fatigue life may be increased by a factor of 100 as a result of treatments applied every 1 percent of the estimated life. The Manson-Coffin relation accurately predicts the prolongation of fatigue life in this case.
Cavitation and Impact Erosion—Concepts, Correlations, Controversies
Authors: Eisenberg P
Published: March 2009

Increasingly severe requirements for materials in modern high performance applications have re-emphasized the need for fundamental understanding of erosion processes associated with cavitation and liquid impingement. In recent years, there has been disclosed a number of concepts which are proving helpful in the description of both types of erosion in a wide range of hostile environments (high temperatures, corrosive liquids, etc.). Such probings are providing a framework for development of useful methods of analysis and prediction of the response of materials under cavitation attack and liquid impact. In spite of the ingenuity of these ideas and investigations, however, the nature of the complex interactions among the many parameters involved inevitably has resulted in controversies which have yet to be resolved.

Perhaps the most important concepts which have made possible rational correlation attempts and show promise of a unified treatment of erosion are those of energy absorption. In both types of erosion, very useful results have been obtained based on static strain energy, but a more complete and critical evaluation of these ideas must await the accumulation of data on behavior of materials at high strain rates. Strain rates of interest are those associated with cavitation bubble collapse and with liquid droplet velocities typical of rain impact on high-speed aircraft and droplets in wet steam or vapor turbines.

Whether cavitation damage descriptions can be treated independently of the manner in which the pressures of collapsing cavities are applied—shock waves or internal jet formation—still requires investigation. Internal jet impact is analogous to droplet impingement. These problems are connected intimately with the hydrodynamics of cavitation bubbles, droplet deformation, and the physical properties of the liquid environment. In the latter connection, recent work in hot liquid alkali metals has added to the background information needed to achieve useful correlations.

The dependence of rate of erosion on exposure time and the existence of definite “zones” of erosion (incubation, accumulation, attenuation, steady state,) now seem clearly established for both cavitation and impingement attack. The mechanisms which account for this behavior, however, whether hydrodynamic, mechanical, metallurgical, or combinations of these, still require clarification. Very impressive correlations have been achieved for data in the so-called steady-state zone using strain energy concepts, but even here there is a question about the “steadiness” of this zone. Phenomenological fatigue theories have been adapted to describe the history of damage progression with good results. Here again further research is required to clarify whether the role assigned to fatigue is truly governing in the context of these theories or whether the correlations based on statistical fatigue theories are physically correct.
Vibratory Tests in Water on the Combined Action of Cavitation and Corrosion
Authors: Schulmeister R
Published: March 2009

Cavitation damage in magnetostriction tests depends primarily on the frequency and amplitude of the oscillation and on the pressure and temperature of the test fluid. The damage is increasing with rising frequency and amplitude; depending upon pressure and temperature it reaches peak values. In water and watery solutions the amount of damage is affected strongly by corrosive influences. In the model setup it is possible to superimpose the influence of corrosion stimulators, corrosion inhibitors, and gases onto specific influences of the device.

The deterioration of materials by cavitation and corrosion is simultaneously depending on many factors; it is not possible to make generally applicable statements on the significanse of the quality of one single influence. If remedies for a particular damage are to be examined, seperate tests are necessary which have been adapted to this particular purpose.
A Statistically Verified Model for Correlating Volume Loss Due to Cavitation or Liquid Impingement
Authors: Hammitt FG , Huang YC , Kling CL , Mitchell TM , Solomon LP
Published: March 2009

Rocket sled data have been used to evaluate statistically best values for threshold velocity and velocity exponent as well as the coefficient n in the relation: MDPR=K(Vsinθ-V0)α/sinnθ It is found that a reasonable assumption for most materials is that threshold velocity is zero, n = 1, and that there is a rough correlation between K and α. The correlations with the data are relatively poor. However, within the basic precision attained, a single figure of merit for the material in terms of either K or α could be derived easily.

A more basic relation for the evaluation of MDPR has been assumed in terms of the energy flux model. In this relation the material properties are described in terms of an energy per volume term describing material failure. It has been found that the material energy term is best described as proportional to ultimate resilience. No correlation with any efficiency term relating liquid and material properties alone has been found.
Hydrodynamic Model of Correlation of Metal Removal Rates from Repetitive Drop Impact
Authors: Pouchot WD
Published: March 2009

There is available from the Central Electricity Generating Board (CEGB) of the United Kingdom information on metal removal by water drops from steam turbine blade materials. By postulating a liquid film on the CEGB specimens, a dimensionless correlation of the data is obtained in terms of both fluid and metal properties. From the correlation it may be concluded that the characteristic changes of erosion rate with normal impact velocity and impinging drop diameter are predominantly hydrodynamic effects working on a material of constant average strength.

The presence or absence of a fluid film on test pieces should be directly observable through strobe lighting and photography. Such an experiment would be a first step in testing the proposed correlation procedure.
Application of the Andreasen Pipet to the Determination of Particle Size Distribution of Portland Cement and Related Materials
Authors: Grindrod PS
Published: March 2009

The procedure for determining particle size distribution and calculating specific surface area of portland cement from Andreasen pipet data is described. Size distribution data are compared with results from the Wagner turbidimeter, Roller analyzer, Haultain Infrasizer, micromesh sieves and woven wire sieves. Surface area calculated from the Andreasen pipet data is compared with values from the Blaine air permeability apparatus. A combination of the techniques of sieve analysis, particle size analysis by sedimentation, and surface area determination by permeameter leads to a size characterization of portland cement.
Use of the Coulter Counter and the Alpine Sieve for Particle Size Analysis of Cement
Authors: Brown OE , Bobrowski GS , Kovall GE
Published: March 2009

The purpose of this study was to determine whether the Coulter counter was an effective means of determining particle size distributions of portland cement. Complete Coulter counter and Alpine sieve analyses were performed on National Bureau of Standards Samples 114-J and 114-K. The data received from the Coulter counter and the Alpine sieve were supplemented by Wagner turbidimeter and Blaine air permeability data on the two samples.

Specific surface area calculations made with Coulter counter and Alpine sieve data agreed remarkably well with similar Blaine data. Wagner data at no time correlated with either Alpine sieve or Blaine air permeability results. Perhaps the Wagner turbidimeter should have been investigated as to its reliability as a particle size distribution or surface area measurement device.

The Coulter counter was found to have primary value in validating Alpine sieve results. The Alpine sieve was found to be useful in getting data much faster and with a higher degree of reliability or repeatability than the Coulter counter, which is very time-consuming to operate, and appears to be the most efficient device used for particle size studies.
The Effect of Stress Ratio During Crack Propagation and Fatigue for 2024-T3 and 7075-T6 Aluminum
Authors: Walker K
Published: March 2009

An effective stress, σ¯ = σmax1-mΔσm where m is assumed to be a material constant, is shown to predict the effect of stress ratio on crack propagation and fatigue life for two aluminum alloys. Simple approximations of notch stress and strain using Neuber's notch rule are introduced to extend the predictions of stress-ratio effects to inelastic notch behavior.
Laboratory Simulation of Structural Fatigue Behavior
Authors: Morrow J , Wetzel RM , Topper TH
Published: March 2009

Designing against fatigue failure involves so many uncertainties that it is usually necessary to test full-scale structures prior to service to prove their reliability. Such tests should be simple, short, and inexpensive. At the same time, it is necessary to insure that the fatigue response of the laboratory test reflects the actual performance that can be expected of the structure in its service environment.

The nominal stresses anticipated in a structure in service are usually known or can be estimated. Mechanics analyses have been developed which can be used with smooth specimens or smooth-specimen data to determine local stresses and strains in terms of known nominal stresses even when the local behavior is inelastic. Two methods of solving for the critical stresses and strains are reviewed and compared using notched- and smooth-specimen fatigue data for representative aircraft metals. The approach based upon Neuber's Rule is the most satisfactory and can easily be used to provide control conditions which cause smooth specimens to imitate the stress-strain response of the metal at a notch root.

It is now possible to understand and predict many aspects of structural fatigue from relatively simple tests of small unnotched specimens. The emphasis on the local stress-strain behavior is sufficiently different from more traditional ways of approaching structural fatigue that more research is needed. Advantages and disadvantages of this new viewpoint are discussed and possible future developments are indicated.
Comparison of Fatigue Lives Under Conventional Program Loading and Digital Random Loading
Authors: Jacoby GH
Published: March 2009

On the basis of a gust-load distribution, evaluated by applying level crossing-counting method, an 8-step program test and tests with a random sequence of stress cycles were performed. The results of these tests are compared with the results of tests with a random sequence of maxima and minima. The latter are based on a distribution of maxima and minima, which were derived from the gust-load distribution splitted in several stationary Gaussian processes. In further tests, ground-air-ground cycles were included in the study. Programmed and randomized flight-by-flight tests were compared.

The results of the study revealed that in the case of steady mean stress and the applied conditions program loading overestimates life by a factor of about 6. In case of flight-by-flight tests, however, the load-time history (either programmed or randomized) seem to be unimportant.
Effect of Oxygen and of Water Vapor on the Fatigue Life of Nickel at 300 C
Authors: Smith HH , Shahinian P
Published: March 2009

The fatigue behavior of high-purity nickel, vibrated in reversed bending, was studied at 300 C in oxygen and in water vapor at pressures from 10-9 to 10 torr. Fatigue life was reduced in both oxygen and water vapor, but the variation in life with pressure differed somewhat for the two. The curve of fatigue life versus oxygen pressure is step-shaped with little or no dependence of life on pressure at very low and high pressures, the major reduction taking place at intermediate pressures. In contrast, the fatigue life in water vapor drops off gradually throughout the entire high-pressure range, but the maximum reduction is much less than in oxygen. Evidence obtained by residual gas analysis shows that a hot ionization gage filament may change the composition of the environment which, in turn, may affect fatigue life. Metallographic examination of failed specimens disclosed a relation between deformation and cracking characteristics and oxygen pressure. A calculation of the pressure required to saturate the crack surfaces at an estimated rate of crack growth showed that the predicted pressure agreed with the highest transition pressure, at which the reduction in fatigue life approaches a maximum.
The Role of Impact Testing in Characterizing the Toughness of Materials
Authors: Matthews WT
Published: March 2009

The objectives of fracture toughness testing are to provide information for design, screening, and acceptance of materials. Several tests are discussed in relation to an ideal design test possessing quantitativeness and generality: slow and impact-loaded Griffith-Irwin fracture mechanics, conventional Charpy, and drop-weight tear testing (DWTT). The features and limitations of these methods are noted. Fracture mechanics is recommended for testing relatively brittle materials and DWTT and associated procedures as the best available for tough materials. Probable increased development in quantitative fracture mechanics including impact testing is discussed. For screening and acceptance, conventional Charpy testing is recommended provided that correlation with more basic tests has been established.
An Evaluation of the Charpy Impact Test
Authors: Harsem Ø , Wintermark H
Published: March 2009

For mild steels intended for service temperatures down to -20 to -30 C it is normal to prescribe a Charpy V-notch test with a minimum requirement of 2.8 kgf∙m. Experience has proved that this is a satisfactory criterion for this type of steel. With regard to steels for lower service temperatures and those with higher tensile strength there is a degree of uncertainty. A minimum impact energy of 3.5 to 4.15 kgf∙m at test temperatures immediately below service temperature often is prescribed.

The investigations described here, cover hot rolled plates from six European steelworks. The materials are from 20 heats (one plate from each) and are intended for welded structures with service temperatures down to -50 C. The steels have an ultimate tensile strength from 47.3 to 67.5 kgf/mm2 and a yield point from 32.1 to 48.9 kgf/mm2.

The nil-ductility transition (NDT) temperature was determined and for the 20 heats lies between -40 and -75 C. Impact tests were carried out as Charpy V-notch tests taken lengthwise (KVL) and transverse (KVT) to the rolling direction. Charpy pressed notch tests also were carried out as longitudinal tests (KPL).

The KVL tests show considerable scattering in the whole temperature range from -15 to -80 C. This tendency to scattering varied greatly from heat to heat. There is no unambiguous correlation between the NDT temperatures and the KVL values. In the transition range the transition curves exhibit two kinks giving the curves an approximate double S-form. This may be interpreted as an expression of bimodality in the range around the kinks. The NDT temperature lies in most cases in the range where the kinks are situated.

The KVT values show considerably less scattering than the KVL values and no tendency to bimodal distribution at the actual test temperatures. An interesting observation is that the KVT values at the respective NDT temperatures of the different steels show very little variation. The average value for all the KVT tests carried out at NDT temperature is 3.21 kgf∙m with a standard deviation of only 0.57 kgf∙m. This seems to indicate that for this type of low temperature steel a criterion based on the KVT value at a constant testing temperature may be applied in order to sort out the steels which have a NDT temperature higher than the testing temperature.

The KPL values generally show little scattering. There is, however, a very marked bimodal distribution over a small temperature range which begins at 30 to 40 C over the NDT temperature.

Microfractographic investigations with extraction replicas taken from just below the base of the notch of KVT specimens show thin discontinuous slag film in the fracture surface. The presence of slag films does not appear to affect the fact that the NDT temperature is independent of the rolling direction but seems to affect the level of the NDT temperature.
Applications of the Instrumented Charpy Impact Test
Authors: Wullaert RA
Published: March 2009

Studies involving the application of the instrumented Charpy impact test are presented. The studies were concerned with the effect of strain rate, alloying, and irradiation on the ductile-brittle transition temperature (DBTT) and fracture behavior of pressure vessel steels.

The effect of strain rate on a 0.02C and 0.02C-3.5Ni steel was evaluated by comparing instrumented Charpy tests with three-point slow bend tests on Charpy V-notch specimens. Increasing the strain rate (1) increased the DBTT, (2) increased the yield stress, and (3) decreased the temperature dependence of the yield stress. The strain rate sensitivity of the yield stress was mainly responsible for the increase in the DBTT.

The instrumented Charpy test was used to determine why small nickel additions to steel are so effective in lowering the ductile-brittle transition temperature. The decrease in the DBTT was shown to be related to the decrease in the strain rate and temperature dependence of the yield stress produced by nickel.

The effect of irradiation on A212-B steel was evaluated by use of the instrumented Charpy impact test. Irradiating A212-B steel at approximately 260 C to a fluence of 9.4 × 1018 n/cm2 (>1 Mev) increased the DBTT 56 C. Irradiation increased the dynamic yield stress 30 percent but reduced the strain rate sensitivity of the yield stress. The increase in the ductile-brittle transition temperature was shown to be almost entirely due to the radiation-induced increase in the dynamic yield stress.
Influence of Inertial Load in Instrumented Impact Tests
Authors: Venzi S , Priest AH , May MJ
Published: March 2009

The effect of inertial loading in instrumented impact tests has been studied, and it is shown that during such tests large errors can be made in calculating the bending stress of a specimen at fracture if inertial loading is not taken into account. By instrumenting the tup, anvil, and specimen it is shown that in the period over which inertial effects occur, there is no simple relationship between the load measured on the tup, anvil, and specimen.

To assist in interpretation and evaluation of impact load-time curves a model has been used which relates the spring constants and masses of the tup and anvil of the test machine and specimen to the frequency, phase, and relative amplitude of the oscillations occurring in the impact test.

The importance of inertial loading is emphasized, in particular, with regard to dynamic measurement of plane strain fracture toughness KIc.
Is Quantitative Metallography Quantitative?
Authors: Moore GA
Published: March 2009

While the basic principles of quantitative metallography have been firmly established, the practice of such measurements yields highly variable results. Simple laws define the statistical limitation on any measuring method. Serious errors arise from improper selection and preparation of specimens. Anticipated gradients must be encompassed by a planned sampling scheme which guarantees unbiased representation and permits measurement of actual variation in the material studied. Specimen preparation must give a truthful image of the structure. Any free choices by the operator introduce bias. The precision of measurement of one micrograph is primarily controlled by a combination of statistical uncertainty and observational error at the edges of particles. The statistical uncertainty conforms to the ideal when the apparent particle size is small, but observation becomes inefficient as the average intercept width increases and the number of particles in the field decreases. Edge errors are maximum with small particles and vary with the observer or the instrument used. Maximum precision is obtained when these two errors are approximately equal. While quantitative metallography is a statistical, rather than exact, process and subject to serious or fatal errors when practiced crudely, carefully controlled measurements can yield several structural parameters with a precision adequate to satisfy any practical metallurgist.
Microcleanliness of Steel—A New Quantitative TV Rating Method
Authors: Rege RA , Forgeng WD , Stone DH , Alger JV
Published: March 2009

A general method for the rating of nonmetallic inclusions in steel by use of a quantitative television microscope (QTM) has been developed. The discussion of the method includes a special automatic specimen preparation procedure and a simplified statistical test to indicate the reliability and precision of the data. Information obtained with the QTM consists of area fraction of inclusions, number of inclusions, and distribution of inclusion lengths. These QTM parameters, or the values derived therefrom, have been used to express the overall inclusion rating for steel products and for comparison with standard rating methods. Steels have been ranked according to cleanliness by values derived from the QTM method similar to the ranking by values derived from inclusion rating methods described in ASTM Designation E 45. The QTM method has been shown to be versatile and to improve reproducibility by eliminating most of the variation due to human judgment.
Application of Fracture Mechanics Technology to Medium-Strength Steels
Authors: Clark WG , Wessel ET
Published: March 2009

A review of fracture toughness and fatigue crack growth rate data currently available for medium-strength steels is presented. Data are included for three commonly used structural steels (AISI 1045, 1144, and 4140); two pressure vessel steels (ASTM A533 Grade B, Class 1 and A216 WCC grade); and three grades of rotor forging steels (ASTM A469, Class 4; A470, Class 8; and A471, Class 4). These data clearly illustrate that under conditions of sufficient restraint to ensure plane strain loading, existing linear elastic fracture mechanics technology is applicable to medium-strength steels. The advantages and overall potential of fracture mechanics technology as a quantitative tool for the prevention of failure is demonstrated by means of an example problem.
Direct-Current Magnetic Measurements for Soft Magnetic Materials
Authors: Dieterly DC , Edgar RF , Fredrick AH , Hale JW , Jones DH , Lamson HW , Mitchell WT , Mundy RE , Owens CD , Beiler AC , Cooter IL , Eberly WS
Published: March 2009

Description

This publication is the second chapter of what will eventually become a comprehensive manual on magnetic testing prepared by a task group of ASTM Committee A-6 on Magnetic Properties. The first chapter was previously published as Magnetic Testing—Theory and Nomenclature, ASTM Special Technical Publication 371.
Achievement of High Fatigue Resistance in Metals and Alloys
Authors: ASTM Committee E-9
Published: March 2009

Description

The Symposium on Achievement of High Fatigue Resistance in Metals and Alloys was given at the Seventy-second Annual Meeting of ASTM held in Altantic City, N. J., 22-27 June 1969. ASTM Committee E09 on Fatigue, Subcommittee I on Research sponsored the symposium, which was held in three sessions: Parameters Important to High Fatigue Resistance, H. F. Hardrath, National Aeronautics and Space Administration, chairman of Session I; Mechanisms for Achieving High Fatigue Resistance, J. C. Grosskreutz, chairman of Session II; and Processes for Achieving High Fatigue Resistance, C. E. Feltner, Ford Motor Co., chairman of Session III. J. C Grosskreutz and C. E. Feltner presided as symposium cochairmen.
Fineness of Cement
Authors: Committee C-1
Published: March 2009

Description

The Symposium on Fineness of Cement was given at the Seventy-first Annual Meeting of ASTM held in San Francisco, Calif., 23—28 June 1968. The sponsor of this symposium was Committee C0l on Cement. G. J. Verbeck, Portland Cement Assn., presided as symposium chairman.
Applications of Modern Metallographic Techniques
Authors: ASTM Committee E-4
Published: March 2009

Description

ASTM Committee E04 on Metallography and the American Society for Metals cosponsored the Symposium on Applications of Modern Metallographic Techniques given on 13 Oct. 1969. The session was presented at the ASM Annual Materials Engineering Exposition and Congress, held in Philadelphia, Pa., 13-16 Oct. 1969. The joint ASTM-ASM venture was arranged by the American Society for Metals, with W. D. Forgeng, Jr., United States Steel Corp., chairman of Committee E04, presiding as symposium chairman.
Irradiation Effects on Structural Alloys for Nuclear Reactor Applications
Authors: Bement AL
Published: March 2009

Description

The Symposium on Irradiation Effects on Structural Alloys for Nuclear Reactor Applications was presented at Niagara Falls, Canada, 29 June-1 July 1970, in conjunction with the Seventy-third Annual Meeting of the American Society for Testing and Materials held in Toronto, Ontario, Canada, 22-26 June 1970. The symposium was sponsored by ASTM Committee E10 on Radiosotopes and Radiation Effects. A. L. Bement, Jr., Battelle Memorial Institute, Pacific Northwest Laboratory, served as chairman of the symposium committee, which consisted of J. Moteff, cochairman, and K. M. Zwilsky, C. J. Baroch, E. Landerman, and L. E. Steele. The six sessions were presided over by L. J. Chockie, D. R. Harries, W. R. Thomas, R. Bullough, J. Moteff, and H. Bohm. Two agenda discussion sessions also were presented to survey the status of two contemporary problem areas.
Functional Recovery of Aimed Scratching Movements after a Graded Proprioceptive Manipulation
Authors: Page Keri L. , Matheson Thomas
Published: March 2009

To demonstrate the role of proprioceptive feedback in aimed limb movements, we induced graded changes in the signals provided by the principal receptor in a leg of a locust. The femoro-tibial chordotonal organ (FCO) of the hindleg monitors extension and flexion movements of the tibia and provides the main source of proprioceptive feedback about tibial kinematics. The FCO apodeme (tendon) was surgically shortened by different amounts to provide a systematic bias to this feedback, and aimed scratching movements were analyzed over the week after surgery. Shortening the apodeme led to increased firing of sensory neurons of the FCO at flexed joint angles and is thus functionally similar to flexing the tibia. Immediately after surgery, limb movements shifted dorsally and posteriorly, driven by overextension of the femoro-tibial joint and changes at other joints of the limb. The extent of tibial overextension reflected the extent of apodeme shortening. Overextension would tend to renormalize the FCO feedback signal and can be explained by known interjoint reflex pathways. Our data demonstrate that proprioceptive feedback provides a graded signal that is used to control these aimed limb movements. Over the course of 7 d after surgery, there was a functional recovery in aiming as the overall patterns of movement returned toward control values driven by reciprocal compensatory changes at two joints. The sensory to motor pathways are monosynaptic and oligosynaptic in this system, thus providing us with a powerful opportunity to investigate further the sensorimotor transformations and plasticity of aimed limb movements.
Neuronal Phenotype in the Mature Nervous System Is Maintained by Persistent Retrograde Bone Morphogenetic Protein Signaling
Authors: Eade Kevin T. , Allan Douglas W.
Published: March 2009

The terminal differentiation of many developing neurons occurs after they innervate their target cells and is triggered by secreted target-derived signals that are transduced by presynaptic cognate receptors. Such retrograde signaling induces the expression of genes that are often distinctive markers of neuronal phenotype and function. However, whether long-term maintenance of neuronal phenotype requires persistent retrograde signaling remains poorly understood. Previously, we demonstrated that retrograde bone morphogenetic protein (BMP) signaling induces expression of a phenotypic marker ofDrosophilaTv neurons, the neuropeptide FMRFamide (FMRFa). Here, we used a genetic technique that spatiotemporally targets transgene expression inDrosophilato test the role of persistent BMP signaling in the maintenance of Tv phenotype. We show that expression of dominant blockers of BMP signaling selectively in adult Tv neurons dramatically downregulated FMRFa expression. Moreover, adult-onset expression of mutant Glued, which blocks dynein/dynactin-mediated retrograde axonal transport, eliminated retrograde BMP signaling and dramatically downregulated FMRFa expression. Finally, we found that BMP deprivation did not affect Tv neuron survival and that FMRFa expression fully recovered to control levels after the termination of BMP blockade or Glued expression. Our results show that persistent retrograde BMP signaling is required to induce and to subsequently maintain the expression of a stably expressed phenotypic marker in a subset of matureDrosophilaneurons. We postulate that retrograde maintenance of neuronal phenotype is conserved in vertebrates, and as a consequence, neuronal phenotype is likely vulnerable to neurodegenerative disease pathologies that disrupt neuronal connectivity or axonal transport.
Thyrotropin-Releasing Hormone Increases Behavioral Arousal through Modulation of Hypocretin/Orexin Neurons
Authors: Hara Junko , Gerashchenko Dmitry , Wisor Jonathan P. , Sakurai Takeshi , Xie Xinmin (Simon) , Kilduff Thomas S.
Published: March 2009

Thyrotropin-releasing hormone (TRH) has previously been shown to promote wakefulness and to induce arousal from hibernation. Expression of TRH-R1 (TRH receptor 1) is enriched in the tuberal and lateral hypothalamic area (LHA), brain regions in which the hypocretin/orexin (Hcrt) cells are located. Because the Hcrt system is implicated in sleep/wake control, we hypothesized that TRH provides modulatory input to the Hcrt cells.In vitroelectrophysiological studies showed that bath application of TRH caused concentration-dependent membrane depolarization, decreased input resistance, and increased firing rate of identified Hcrt neurons. In the presence of tetrodotoxin, TRH induced inward currents that were associated with a decrease in frequency, but not amplitude, of miniature postsynaptic currents (PSCs). Ion substitution experiments suggested that the TRH-induced inward current was mediated in part by Ca2+influx. Although TRH did not significantly alter either the frequency or amplitude of spontaneous excitatory PSCs, TRH (100 nm) increased the frequency of spontaneous inhibitory PSCs by twofold without affecting the amplitude of these events, indicating increased presynaptic GABA release onto Hcrt neurons. In contrast, TRH significantly reduced the frequency, but not amplitude, of miniature excitatory PSCs without affecting miniature inhibitory PSC frequency or amplitude, indicating that TRH also reduces the probability of glutamate release onto Hcrt neurons. When injected into the LHA, TRH increased locomotor activity in wild-type mice but not inorexin/ataxin-3mice in which the Hcrt neurons degenerate postnatally. Together, these results are consistent with the hypothesis that TRH modulates behavioral arousal, in part, through the Hcrt system.
The Nucleus Retroambiguus Control of Respiration
Authors: Subramanian Hari H. , Holstege Gert
Published: March 2009

The role of the nucleus retroambiguus (NRA) in the context of respiration control has been subject of debate for considerable time. To solve this problem, we chemically (usingd,l-homocysteic acid) stimulated the NRA in unanesthetized precollicularly decerebrated cats and studied the respiratory effect via simultaneous measurement of tracheal pressure and electromyograms of diaphragm, internal intercostal (IIC), cricothyroid (CT), and external oblique abdominal (EO) muscles. NRA-stimulation 0–1 mm caudal to the obex resulted in recruitment of IIC muscle and reduction in respiratory frequency. NRA-stimulation 1–3 mm caudal to the obex produced vocalization along with CT activation and slight increase in tracheal pressure, but no change in respiratory frequency. NRA-stimulation 3–5 mm caudal to the obex produced CT muscle activation and an increase in respiratory frequency, but no vocalization. NRA-stimulation 5–8 mm caudal to the obex produced EO muscle activation and reduction in respiratory frequency. A change to the inspiratory effort was never observed, regardless of which NRA part was stimulated. The results demonstrate that NRA does not control eupneic inspiration but consists of topographically separate groups of premotor interneurons each producing detailed motor actions. These motor activities have in common that they require changes to eupneic breathing. Different combination of activation of these premotor neurons determines the final outcome, e.g., vocalization, vomiting, coughing, sneezing, mating posture, or child delivery. Higher brainstem regions such as the midbrain periaqueductal gray (PAG) decides which combination of NRA neurons are excited. In simple terms, the NRA is the piano, the PAG one of the piano players.
Dopamine DRD2 Polymorphism Alters Reversal Learning and Associated Neural Activity
Authors: Jocham Gerhard , Klein Tilmann A. , Neumann Jane , von Cramon D. Yves , Reuter Martin , Ullsperger Markus
Published: March 2009

In humans, presence of an A1 allele of theDRD2/ANKK1-TaqIapolymorphism is associated with reduced expression of dopamine (DA) D2receptors in the striatum. Recently, it was observed that carriers of the A1 allele (A1+ subjects) showed impaired learning from negative feedback in a reinforcement learning task. Here, using functional MRI (fMRI), we investigated carriers and noncarriers of the A1 allele while they performed a probabilistic reversal learning task. A1+ subjects showed subtle deficits in reversal learning. In particular, these deficits consisted of an impairment in sustaining the newly rewarded response after a reversal and in a generally decreased tendency to stick with a rewarded response. Both genetic groups showed increased fMRI signal in response to negative feedback in the rostral cingulate zone (RCZ) and anterior insula. Negative feedback that incurred a change in behavior additionally engaged the ventral striatum and a region of the midbrain consistent with the location of dopaminergic cell groups. The response of the RCZ to negative feedback increased as a function of preceding negative feedback. However, this graded response was not observed in the A1+ group. Furthermore, the A1+ group also showed diminished recruitment of the right ventral striatum and the right lateral orbitofrontal cortex (lOFC) during reversals. Together, these results suggest that a genetically driven reduction in DA D2receptors leads to deficient feedback integration in RCZ. This, in turn, was accompanied by impaired recruitment of the ventral striatum and the right lOFC during reversals, which might explain the behavioral differences between the genetic groups.
Raphé Neurons Stimulate Respiratory Circuit Activity by Multiple Mechanisms via Endogenously Released Serotonin and Substance P
Authors: Ptak Krzysztof , Yamanishi Tadashi , Aungst Jason , Milescu Lorin S. , Zhang Ruli , Richerson George B. , Smith Jeffrey C.
Published: March 2009

Brainstem serotonin (5-HT) neurons modulate activity of many neural circuits in the mammalian brain, but in many cases endogenous mechanisms have not been resolved. Here, we analyzed actions of raphé 5-HT neurons on respiratory network activity including at the level of the pre-Bötzinger complex (pre-BötC) in neonatal rat medullary slicesin vitro, and in the more intact nervous system of juvenile rats in arterially perfused brainstem–spinal cord preparationsin situ. At basal levels of activity, excitation of the respiratory network via simultaneous release of 5-HT and substance P (SP), acting at 5-HT2A/2C, 5-HT4, and/or neurokinin-1 receptors, was required to maintain inspiratory motor output in both the neonatal and juvenile systems. The midline raphé obscurus contained spontaneously active 5-HT neurons, some of which projected to the pre-BötC and hypoglossal motoneurons, colocalized 5-HT and SP, and received reciprocal excitatory connections from the pre-BötC. Experimentally augmenting raphé obscurus activity increased motor output by simultaneously exciting pre-BötC and motor neurons. Biophysical analysesin vitrodemonstrated that 5-HT and SP modulated background cation conductances in pre-BötC and motor neurons, including a nonselective cation leak current that contributed to the resting potential, which explains the neuronal depolarization that augmented motor output. Furthermore, we found that 5-HT, but not SP, can transform the electrophysiological phenotype of some pre-BötC neurons to intrinsic bursters, providing 5-HT with an additional role in promoting rhythm generation. We conclude that raphé 5-HT neurons excite key circuit components required for generation of respiratory motor output.
Gonadal Steroids Maintain 24 h Acetylcholine Release in the Hippocampus: Organizational and Activational Effects in Behaving Rats
Authors: Mitsushima Dai , Takase Kenkichi , Funabashi Toshiya , Kimura Fukuko
Published: March 2009

Extracellular acetylcholine (ACh) levels in the dorsal hippocampus increases during learning or exploration, exhibiting a sex-specific 24 h release profile. To examine the activational effect of gonadal steroid hormones on the sex-specific ACh levels and its correlation with spontaneous locomotor activity, we observed these parameters simultaneously for 24 h. Gonadectomy severely attenuated the ACh levels, whereas the testosterone replacement in gonadectomized males or 17β-estradiol replacement in gonadectomized females successfully restored the levels. 17β-Estradiol-priming in gonadectomized males could not restore the ACh levels, and testosterone replacement in gonadectomized females failed to raise ACh levels to those seen in testosterone-primed gonadectomized males, revealing a sex-specific activational effect. Spontaneous locomotor activity was not changed in males by gonadectomy or the replacement of gonadal steroids, but 17β-estradiol enhanced the activity in gonadectomized females. Gonadectomy severely reduced the correlation between ACh release and activity levels, but the testosterone replacement in gonadectomized males or 17β-estradiol replacement in gonadectomized females successfully restored it. To further analyze the sex-specific effect of gonadal steroids, we examined the organizational effect of gonadal steroids on the ACh release in female rats. Neonatal testosterone or 17β-estradiol treatment not only increased the ACh levels but also altered them to resemble male-specific ACh release properties without affecting levels of spontaneous locomotor activity. We conclude that the activational effects of gonadal steroids maintaining the ACh levels and the high correlation with spontaneous locomotor activity are sex-specific, and that the organizational effects of gonadal steroids suggest estrogen receptor-mediated masculinization of the septo-hippocampal cholinergic system.
A Single Intra-PFC Infusion of BDNF Prevents Cocaine-Induced Alterations in Extracellular Glutamate within the Nucleus Accumbens
Authors: Berglind William J. , Whitfield Timothy W. , LaLumiere Ryan T. , Kalivas Peter W. , McGinty Jacqueline F.
Published: March 2009

The glutamatergic pathway arising in the dorsomedial prefrontal cortex (dmPFC) and projecting to the nucleus accumbens (NAc) core is a critical component of the reward circuitry that underlies reinstatement to cocaine-seeking behavior. Brain-derived neurotrophic factor (BDNF) is expressed by and modulates PFC–NAc neurons. BDNF infusion into the dmPFC attenuates reinstatement to cocaine-seeking behavior, as well as some cocaine-induced molecular adaptations within the NAc. In the present study, it is demonstrated that a single intra-dmPFC infusion of BDNF prevents cocaine self-administration-induced reduction in basal extracellular glutamate, as well as cocaine prime-induced increases in extracellular glutamate levels within the NAc. These data suggest that intra-PFC BDNF attenuates reinstatement to cocaine-seeking behavior by normalizing cocaine-induced neuroadaptations that alter glutamate neurotransmission within the NAc.
A Pattern Approach to Mobile Interaction DesignDie Verwendung von Patterns beim Entwerfen mobiler Applikationen
Authors: Grill Thomas , Biel Bettina , Gruhn Volker
Published: March 2009

There are many limitations and benefits of mobile technology and the specific situation of mobile users adds complexity through additional parameters that designers need to address. This makes designing user interfaces and user interaction for mobile applications a very complex task. To address this complexity we propose an interaction design approach using patterns for mobile interaction design. We present an iterative user centered development process which integrates the usage of an interaction pattern library within the interaction design process. By using the pattern approach, not only functional and interaction requirements but also architectural issues are considered. In addition we present tools for designers that enable them to use the pattern library according to the categorization of functionality and interaction representing the dimensions of a design task especially in mobile environments. The proposed method guides developers in their task to design interaction that matches the project´s requirements.
Ghrelin levels are decreased in non-obese prepubertal children born large for gestational age
Authors: Darendeliler Feyza , Poyrazoglu Sukran , Bas Firdevs , Sancakli Ozlem , Gokcay Gulbin
Published: March 2009

Background

Ghrelin is the natural ligand of GH secretagogue receptor. It has several metabolic functions including regulation of food intake, energy homeostasis, and body weight. An inverse relationship between fasting plasma ghrelin and insulin concentrations has been shown. Being born large for gestational age (LGA) has an increased risk of developing insulin resistance.

Objective

The aim of this study was to evaluate ghrelin levels in LGA born children who have no obesity at prepubertal ages and the effect of intrauterine and postnatal growth on ghrelin levels.

Patients and methods

Thirty-two (17F, 15M) LGA born non-obese children (mean (±s.e.m.) age 4.4±0.3 years) were evaluated with respect to glucose, insulin, and ghrelin levels. Their data were compared with that of non-obese 45 (19F, 26M) appropriate for gestational age (AGA) children (mean (±s.e.m.) age 4.0±0.1 years).

Results

LGA children, who had similar age and body mass index (BMI) standard deviation score (SDS) as AGA children, had significantly higher insulin (P=0.044) and at a borderline significance higher homeostasis model assessment-insulin resistance levels (P=0.054) than AGA children. Ghrelin level was significantly lower in LGA born than AGA born children (P=0.001) even after controlling for age, sex, and BMI (P=0.006). There were no differences between genders in insulin and ghrelin levels. Multivariate analysis revealed that birth weight was the only significant parameter influencing ghrelin levels (R2=0.13, B=−0.007, P=0.002).

Conclusions

LGA born non-obese prepubertal children have lower ghrelin levels when compared with age and BMI matched AGA children. Birth weight seems to have the only significant effect on the reduced ghrelin levels.