Decrease In Peak Value Research Articles

Sensitivity study on depressurized LOFC accidents with failure of RCCS in a modular gas-cooled reactor

A modular gas-cooled reactor design with a thermal output of 600 MWt and a core exit temperature of 950 °C has been designed by the Korea Atomic Energy Research Institute based on the GT-MHR reactor concept which adopts a prismatic core. A sensitivity study on the transient plant behavior during a postulated depressurized LOFC accident concurrent with the failure of the RCCS was performed. In the transient analysis, the GAMMA+ code which can handle multi-dimensional, multicomponent problems was used. The RCCS is a passive system which is very reliable and supplies a significant heat removal mechanism during abnormal conditions in a GCR. To investigate the safety characteristics of a GCR under the one of the worst accidental scenarios, a simultaneous failure of the RCCS with a depressurized LOFC was assumed. The thermal behavior of the reactor system was analyzed in various conditions. It is found that the maximum temperature of the reactor fuel compact could exceed 1600 °C at about 50 h at the condition of a depressurized LOFC with a failure of the RCCS. A problem with the structural integrity of the reactor pressure vessel could also be a critical factor. The insulation of a reactor cavity wall serves as a dominant obstacle against a heat transfer from the reactor vessel to the surrounding ground when the RCCS fails to operate. Without insulation material on the reactor cavity wall, the gradients of the increasing rate of the maximum temperature diminish and the peak values decrease. The maximum temperatures of the fuel compact and the reactor vessel are less sensitive to the concrete and surrounding soil properties, those are the thermal conductivity and volumetric heat capacity, when the insulation material is used. The uncertainties in the properties of the concrete and the surrounding soil become significant without an insulation material in the cavity. To improve the safety of a modular GCR, more effective and feasible heat removal mechanism need to be devised based on the comprehensions on the heat transfer characteristics.

Optical properties of the micro/nano structures of Morpho butterfly wing scales

The micro/nano structures of the wing scales in Morpho butterfly are responsible for the structural coloration, with a major part ascribed to interference and diffraction of light. The optical properties of the butterfly wings were investigated by simulating a two-dimensional model using rigorous coupled-wave analysis technique. It is proved that they depend strongly on the structural parameters, incidence angle and refractive index. The peak value and the peak wavelength of the reflection efficiency increase as the vertical periodic thickness increases. The peak value decreases observably, while both of the bandwidth and the peak wavelength increase when the number of the vertical periods decreases. Increase of the horizontal periodic width causes a decrease of the peak value and an increase of the peak wavelength, although the variations are small. The peak value decreases distinctly and the peak wavelength increases as the ambient refractive index increases, which corresponds to the variation in ambient conditions. The research reveals the mechanisms of the brilliant structural color in Morpho butterfly, and is of great significance to the design, manufacture and applications of the bionic micro/nano structures for gas detection.

Kelvin-Helmholtz billows and their effects on mean state during gravity wave propagation

Abstract. The Kelvin-Helmholtz (KH) billows which appear in the process of gravity wave (GW) propagation are simulated directly by using a compressible nonlinear two-dimensional gravity wave model. The differences between our model and others include: the background field has no special initial configuration and there is no initial triggering mechanism needed in the mesosphere and lower thermosphere (MLT) region to excite the KH billows. However, the initial triggering mechanism is performed in the lower atmosphere through GW, which then propagate into the MLT region and form billows. The braid structures and overturning of KH billows, caused by nonlinear interactions between GWs and mean flow, can be resolved precisely by the model. These results support the findings in airglow studies that GWs propagating from below into the MLT region are important sources of KH billows. The onset of small scale waves and the wave energy transfer induce the shallower vertical wave number power spectral densities (PSD). However, most of the slopes are steeper than the expected kz−3 power law, which indicates that GWs with 10 km vertical wavelength are still a dominant mode. The results also show that the evolution of mean wind vary substantially between the different processes of GWs propagation. Before the KH billows evolve, the mean wind is accelerated greatly by GWs. By contrast, as the KH billows evolve and mix with mean flow, the mean wind and its peak value decrease.

Indirect voltammetric determination of caffeine content in coffee using 1,4-benzoquinone modified carbon paste electrode

In this paper a simple and highly sensitive electroanalytical method for the determination of caffeine content using 1,4-benzoquinone modified carbon paste electrode is presented. The method is based on suppression of 1,4-benzoquinone peak current on addition of caffeine. Square-wave and cyclic voltammetric techniques were utilised for the investigation. The 1,4-benzoquinone modified electrode exhibited a well-defined peak with reproducible peak current values for repetitive measurements; and showed a decrease in peak current value with an increase in caffeine content. The result revealed two linear range regions between 0 mmol L −1 and 0.5 mmol L −1 and 0.5 mmol L −1 and 8.0 mmol L −1, with detection limits of 0.3 μmol L −1 and 5.1 μmol L −1, respectively. The method was then successfully applied to the determination of caffeine content in coffee samples. The effects of pH, electrode composition, step potential, pulse amplitude and square-wave frequency on the voltammetric responses were also investigated.

Network competition in a resin-modified glass-ionomer cement

Attempts have been made to improve the mechanical properties and convenience of use of glass-ionomer cement (GIC) by various modifications, in particular by including a free radical-polymerizable component (“resin-modified” GIC, RMGIC). Necessarily, the one replaces part of the other, but the chemistry suggests that the formation of each network separately would inhibit diffusion and thus the other reaction. Objective To ascertain whether interference occurs between the components of an RMGIC by variation of the irradiation regime. Materials and methods Cylindrical specimens (6 mm × 3 mm diameter) of one brand of RMGIC (Shades A3, D2; Fuji II LC, GC; capsules) were prepared in ptfe moulds. After machine-mixing for 10 s, each of the three increments was irradiated from the top for various times (0–60 s). In addition, extra irradiation from the bottom; from the bottom before, and from the side after, ejection from the mould; the same using two curing lamps; and at various delays after mixing (0–18 h), with four replicates of each. After exposure, or as appropriate, specimens were wrapped tightly in aluminium foil for dry storage in the dark at 37 °C for testing at 24 h after mixing. Specimens with evident defects were replaced before testing. Results No increase in strength was found beyond the recommended 20-s irradiation, indeed further exposure reduced the strength. For top-only irradiation, strength rose from the unirradiated value (66 ± 9 MPa) to a peak at 20 s (215 ± 25 MPa), after which it declined steadily. Adding bottom irradiation gave a small decrease in peak value (194 ± 36 MPa); adding side irradiation reduced it substantially (113 ± 7 MPa). Delay for 2 min gave a marked reduction (155 ± 15 MPa), declining to the unirradiated value at 18 h (70 ± 15 MPa). No effect due to shade was detected. Significance Competition between network-forming reactions leads to a sensitive balance between the two, and a critical optimum irradiation: too much may be detrimental, as is delay. The essential compromise involved in such mixed chemistry jeopardizes reliability. It is advisable to follow the duration of exposure prescribed by the manufacturer to achieve optimal performance.

Enhanced mid-infrared transmission in heavily doped n-type semiconductor film based on surface plasmons

Transmission of electromagnetic wave in a heavily doped n-type GaAs film is studied theoretically. From the calculations, an extraordinary transmission of p-polarized waves through the film with subwavelength grooves on both surfaces at mid-infrared frequencies is found. This extraordinary transmission is attributed to the coupling of the surface-plasmon polariton modes and waveguide modes. By selecting a set of groove parameters, the transmission is optimized to a maximum. Furthermore, the transmission can be tuned by dopant concentrations. As the dopant concentration increases, the peak position shifts to higher frequency but the peak value decreases.

Prompt-NO formation in methane/oxygen/nitrogen flames seeded with oxygenated volatile organic compounds: Methyl ethyl ketone or ethyl acetate

In the present work, CH and NO profiles are determined using laser-induced fluorescence (LIF) measurements in eight low-pressure laminar flames of CH 4/O 2/N 2 containing various amounts of methyl ethyl ketone or ethyl acetate with respect to the equivalence ratio. Relative CH LIF signals are calibrated using cavity ring-down spectroscopy (CRDS), while NO LIF calibration is performed in the burned gases of NO seeded flames. Temperature measurements are obtained using a coated Pt/Rh thermocouple and serve as temperature profiles input for Chemkin modeling. Volatile organic compound (VOC) submechanisms, previously validated upon major and intermediate species profiles measured using sampling techniques, are incorporated into the GDF-Kin 3.0_NCN for the CH 4 oxidation. This mechanism is adjusted and validated to predict the effect of VOCs seeding on CH and NO formation. It takes into account not only the CH and NO profiles but those previously measured. When methane is replaced by either MEK or EA, the NO mole fraction in the burned gases and the CH peak value are found to jointly decrease, indicating that NO is mainly formed according to the prompt-NO mechanism. According to the kinetic analysis, the VOC impact on NO formation is demonstrated. It is shown that CH radical formation, through the C1 sequence, mainly involves the CH 3 radical, which is formed with the same propensity by one molecule of methane, MEK, or EA. Due to the methane replacement by VOC while the equivalence ratio is maintained constant, we found that the CH peak value decrease follows the total fuel volumetric flow rate decrease, yielding, an NO decrease in the burned gases.

Symmetric loading of a Griffith crack by transient concentrated forces in an orthotropic material

Body forces are used to model the effect of fasteners and stiffeners. This paper contains results of a study that was undertaken to examine the effect of symmetric impact loading by concentrated body forces on a Griffith crack located in an orthotropic material. The integral transform method along with certain potential functions was used to obtain expressions for the stress intensity factor (SIF). Four different loading cases were considered. Numerical calculations show the typical overshoot in the dynamic SIF reaching values as much as 22% of the corresponding static SIF. The magnitude of the overshoot is affected by the material properties as well as the relative position between the crack and the body forces. In fact as the distance between the application of the body force and the crack increases, the magnitude of the peak value decreases. In addition, as the relative distance increases, the time at which the peak value of the overshoot occurs increases. Furthermore, the time interval over which the overshoot is maintained increases as the relative position increases. The results of the study imply that for stiffened or fastened orthotropic materials, the location of the fasteners or stiffeners may significantly affect the stress intensity factors.

Altitude effects on UV spectral irradiance deduced from measurements at Lauder, New Zealand, and at Mauna Loa Observatory, Hawaii

Measurements from Lauder, New Zealand, and from the high‐altitude Mauna Loa Observatory, Hawaii, are used to determine the altitude effects on spectral UV irradiance and to relate these altitude differences to other factors that influence UV radiation. The measured ratios UVMauna Loa/UVLauder are complex functions of both wavelength and solar zenith angle (SZA). Spectrally, the ratios tend to increase toward shorter wavelengths through most of the UV‐A region. For small SZA (SZA < ∼40°) the ratios continue to increase as wavelength decreases throughout the UV‐B region. For SZA = 60° a local maximum occurs in the UV‐B region. As the SZA increases, this turning point moves to longer wavelengths and its peak value decreases. For SZA >∼80°, local minima in the ratios are seen at shorter wavelengths in the UV‐B region. For biologically weighted irradiances, the peak ratios occur near SZA = 70°, where UV‐A, erythemally weighted UV, UV‐B, and DNA‐weighted UV irradiances at Mauna Loa Observatory exceeded those at Lauder by ∼17%, 26%, 27%, and 29% respectively. The ratios of irradiances at the two altitudes, as functions of SZA and wavelength, were related to differences expected from radiative transfer calculations. For small SZA, modeled and measured ratios agreed within the limits of experimental uncertainty without taking differences in altitude distributions of ozone and temperature into account. However, for larger SZA and shorter wavelengths these profile shapes had a significant effect. In the model calculations, satisfactory agreement with the measurements was achieved only when the contribution from radiation scattered from air or cloud tops below the observation height at Mauna Loa Observatory was included. To model this accurately, a three‐dimensional radiative transfer code should be used in conjunction with a topographical model of the surrounding terrain.

Trends in ground level ozone concentrations in the European Union

Following the Council Directive 92/72/EEC on air pollution by ozone the Member States of the European Union have to inform the European Commission on ozone concentrations and exceedances of threshold values within their territory. Using the available information covering the period of 5 years (1994–1998), the data has been analysed for a possible trend in statistical parameters (50- and 98-percentiles) and number and severity of exceedances. Time series are relatively short but the data suggest that there might be a small increasing trend in the 50 percentile values. The ozone peak values, expressed as 98-percentile values or as number of exceedance days tend to decrease. However, these conclusions must be interpreted carefully as on the short time scales considered here meteorological variations and inter-annual changes may play an important role. The decrease in peak values is most likely caused by the decrease in European ozone precursor emissions since 1990; insufficient data is available to explain the increasing 50-percentile values. Possible explanations are an increase in tropospheric ozone background values caused by a world-wide increase in CH 4 , CO and NO x emissions or a reduced ozone titration by reduced NO x emissions on the local scale. The data submitted under the ozone directive is insufficient to provide firm conclusions on this point.

Attachment process in rocket‐triggered lightning strokes

In order to study the lightning attachment process, we have obtained highly resolved (about 100 ns time resolution and about 3.6 m spatial resolution) optical images, electric field measurements, and channel‐base current recordings for two dart leader/return‐stroke sequences in two lightning flashes triggered using the rocket‐and‐wire technique at Camp Blanding, Florida. One of these two sequences exhibited an optically discernible upward‐propagating discharge that occurred in response to the approaching downward‐moving dart leader and connected to this descending leader. This observation provides the first direct evidence of the occurrence of upward connecting discharges in triggered lightning strokes, these strokes being similar to subsequent strokes in natural lightning. The observed upward connecting discharge had a light intensity one order of magnitude lower than its associated downward dart leader, a length of 7–11 m, and a duration of several hundred nanoseconds. The speed of the upward connecting discharge was estimated to be about 2 × 107 m/s, which is comparable to that of the downward dart leader. In both dart leader/return‐stroke sequences studied, the return stroke was inferred to start at the point of junction between the downward dart leader and the upward connecting discharge and to propagate in both upward and downward directions. This latter inference provides indirect evidence of the occurrence of upward connecting discharges in both dart leader/return‐stroke sequences even though one of these sequences did not have a discernible optical image of such a discharge. The length of the upward connecting discharges (observed in one case and inferred from the height of the return‐stroke starting point in the other case) is greater for the event that is characterized by the larger leader electric field change and the higher return‐stroke peak current. For the two dart leader/return‐stroke sequences studied, the upward connecting discharge lengths are estimated to be 7–11 m and 4–7 m, with the corresponding return‐stroke peak currents being 21 kA and 12 kA, and the corresponding leader electric field changes 30 m from the rocket launcher being 56 kV/m and 43 kV/m. Additionally, we note that the downward dart leader light pulse generally exhibits little variation in its 10–90% risetime and peak value over some tens of meters above the return‐stroke starting point, while the following return‐stroke light pulse shows an appreciable increase in risetime and a decrease in peak value while traversing the same section of the lightning channel. Our findings regarding (1) the initially bidirectional development of return‐stroke process and (2) the relatively strong attenuation of the upward moving return‐stroke light (and by inference current) pulse over the first some tens of meters of the channel may have important implications for return‐stroke modeling.

Third harmonic AC susceptibility in superconducting powder

The third harmonic AC susceptibility is theoretically investigated by numerically solving Campbell's model in which the effect of the reversible fluxoid motion is taken into account. According to the calculated result of the AC field amplitude dependence of real and imaginary parts, their peak values decrease and the peak AC field amplitude shifts to higher values when the fluxoid motion changes from irreversible to reversible. This is quite different from the prediction of Bean's critical state model in which the peak value and the peak AC magnetic field are predicted to be constant. Since the reversible phenomenon is expected to be remarkable in superconductors with small sizes, the third harmonic AC susceptibility measurement was carried out for a superconducting powder of alkali metal doped fullerene. Experimental results can be qualitatively explained by the theoretical results. >

Release of peripheral blood progenitor cells during standard dose cyclophosphamide, epidoxorubicin, 5-fluorouracil regimen plus granulocyte colony stimulating factor for breast cancer therapy

High dose chemotherapy with the support of peripheral blood progenitor cells (PBPC) is increasingly used in the treatment of solid tumors. Although the best method of PBPC mobilization is still under investigation, it should be optimized for different tumor types to obtain antitumor effect and mobilizing activity. The authors report these results in terms of the number of PBPC released and the time of maximum mobilization induced by standard dose cyclophosphamide, epidoxorubicin, 5-fluorouracil (CEF) (cyclophosphamide 600 mg/m2, epidoxorubicin 60 mg/m2, 5-fluorouracil 600 mg/m2) plus granulocyte colony stimulating factor (G-CSF) in patients with breast cancer. Peripheral blood progenitor cells were studied by clonogenic assay of granulocyte macrophage colony-forming units (CFU-GM), megakaryocyte colony-forming unit (CFU-Meg) and erythrocyte burst-forming unit (BFU-E) and by flow cytometric analysis of CD34+ cells in 12 patients with early breast cancer throughout three cycles of CEF chemotherapy plus G-CSF. Colony assays and CD34+ cell determination were performed on 111 and 151 blood samples, respectively. The peak of CFU-GM and CD34+ cells occurred consistently at day 11 throughout all three cycles. At day 11 of the first cycle, the median peak values were 2223 CFU-GM/mL and 256 CD34+ cells/microL. A progressive decrease in peak value from the first to the third cycle was observed. Standard dose CEF chemotherapy plus G-CSF is a disease specific regimen allowing PBPC mobilization without any relevant toxicity. Maximum mobilization was recorded at day 11 of the first cycle.

EFFECT OF IMPURITIES ON INCOMMENSURATE PHASE TRANSITION OF K2ZnCl4 CRYSTAL

The soliton behavior of K2ZnCl4 crystal near commensurate-incommensurate phase transition point is investigated by dielectric measurement. It is found that the dielectric curve deviate from Curie-Weiss law and the dielectric peak value decrease with the increasing of the impurities. The influence of impurities on phase transition point Tch in heating run is larger than phase transition point Tcc in cooling run. This phenomenon is contrary to the case of Rb2ZnCl4 crystal. The linear and nonlinear response of a multisoliton lattice is well described by a Landau-type theory. Analysis shows that the thermal hysteresis is mainly determined by the action of impurities, but this does not imply that the Peierls lattice pinning potential may not play any role in the thermal hysteresis.

Impaired response of growth hormone-releasing hormone (GHRH) measured in plasma after L-dopa stimulation in patients with idiopathic delayed puberty.

In order to investigate the regulation of GH secretion in patients with idiopathic delayed puberty (IDP), either prepubertal (stage P1) or early pubertal (P2), GHRH levels in plasma were measured after stimulation with L-Dopa in a group of 16 patients with IDP. The results were compared to those obtained in 12 patients with constitutional short stature (CSS) at the same stages of puberty, who underwent L-Dopa test for insufficient height. Plasma GHRH levels were measured, after extraction and concentration on C18 Sep Pack columns, by radioimmunoassay using an antibody against 1-40 GHRH, which cross-reacts 100% with 1-44 GHRH. The sensitivity of the assay is 6-8 pg/ml. After L-Dopa intake, the peak of GH was mean +/- SEM 8.6 +/- 1.4 ng/ml in IDP and 12.0 +/- 0.8 ng/ml in CSS (NS). The peak of GHRH after L-Dopa was 41 +/- 10 pg/ml in IDP and 96 +/- 25 pg/ml in CSS (p less than 0.02). A significant (p less than 0.02) decrease of plasma GHRH peak values (mean +/- SEM 17.3 +/- 4.4 pg/ml) was noted in the five patients with IDP whose growth velocity was below -2 SD for their bone age compared to the patients with normal growth velocity (mean +/- SEM 75.0 +/- 14.5 pg/ml). These results suggest a hypothalamic dysfunction in patients with IDP, and a relationship between the well-known partial and transitory somatotropic deficiency found in some adolescents having a pubertal delay and their secretion of the releasing hormone GHRH.

Reflection characteristics of torsional waves in a semi-infinite cylindrical rod connected to an elastic half-space

Reflection characteristics of torsional waves in a semi-infinite rod connected to an elastic half-space are analyzed under two specific incident pulse loads, applying Laplace transformations with respect to time and numerical inverse Laplace transformations. The time histories of the torsional stress and rotation of the semi-infinite rod at an arbitrary point are shown. The advantage of this method, i.e., applying the numerical inverse Laplace transformations, is that it is simpler than using Fourier analysis and synthesis, and applicable to any incident pulse load except where the rise time interval of the incident pulse load is too short. In the case of a step pulse load, the stress curves approach that of the fixed boundary condition and the rotation curves approach asymptotically the static rotation value of each given shear modulus ratio GR/G and velocity ratio K. In the case of a half-sine pulse load, the reflected stress peak values decrease and those of the rotation increase with an increase in GR/G and K. A cross−over effect occurs when GR/G≳1 and K≳1; it becomes pronounced as GR/G and K increase.

Optical properties of LPCVD aB (H)

Amorphous boron-hydrogen alloys (9 to 24 at % H) have been prepared and optical properties determined. In the ir, the only bands observed involving H are the B-H stretch at 2560 cm −1 and the B-H bend at 1108 cm −1; no evidence is found for bands associated with BH 2 groupings or H three-center bonds. In the visible-near uv, the ϵ 2 spectrum for the sample with 9 at % H has a broad maximum near 5eV with a peak value of 6. With increasing H content, both optical gap and ϵ 2 peak move to higher energies, while the ϵ 2 peak value and refractive index decrease.

Developments in the Use of Acoustic Shock Pulses in the Study of Elastic Properties of Solids

A nondestructive method of measurement is being developed for the purpose of investigation of the dynamic behavior of solids, especially concerned with nonlinear elasticity. In this paper, we discuss a method of generation of reproducible acoustic shock pulses in various solids, and also discuss the measurements of the stress-strain relationship using intensive acoustic shock pulses. Results obtained are the following: In aluminum samples, a linear relationship between stress and strain is found experimentally for acoustical pressures up to 130 bar before annealing and also up to 65 bar after annealing. On the other hand, after annealing the specimens, we found a variation of pulse shape and a decrease of peak value compared with the pulse shape before annealing. A qualitative discussion is given of photographs of changes in the shapes of the shock pulses that have propagated through solids.