bluuebunny/crossref_metadata_2025 huggingface dataset:
INTERMEDIATELY COUPLED PHONON AND CHARGE FLUCTUATION INDUCED SUPERCONDUCTIVITY IN MgB2 PROBED BY A THREE SQUARE WELL APPROACH
Authors: VARSHNEY DINESH , NAGAR M. , SINGH R. K.
Published: June 2008

A three square well model is developed, which allows one to easily calculate the correlation between the coupling strength parameters and superconducting transition temperature (T c ), pressure and volume derivative of T c and isotope effect exponent for MgB 2. Upon considering the three interactions, namely, electron-phonon, electron-plasmon and Coulomb, the analytical solutions for the energy gap equation allow us to understand the relative interplay of these interactions. The values of the coupling strength and of the Coulomb interaction parameter indicate that the superconductor is in the intermediate coupling regime. The superconducting transition temperature of MgB 2 for the 2D band is estimated as 41 K for [Formula: see text] and μσ*≈0.28. We present correlation curves of T c with various coupling strengths as electron-phonon [Formula: see text], electron-plasmon [Formula: see text] and the Coulomb screening parameter (μσ*). The present approach also explains the reported boron isotope effect and the pressure derivative of T c in the test material. We suggest from these results that both the plasmons and phonons within the framework of a three square well scheme consistently explain the effective electron-electron interaction leading to superconductivity in MgB 2. The implications of the effective interactive potential with both σ and π carriers and its analysis are discussed.
AlSb THIN FILMS PREPARED BY DC MAGNETRON SPUTTERING AND ANNEALING
Authors: CHEN WEIDONG , FENG LIANGHUAN , LEI ZHI , ZHANG JINGQUAN , YAO FEFE , CAI WEI , CAI YAPING , LI WEI , WU LILI , LI BING , ZHENG JIA-GUI
Published: June 2008

Aluminum antimonide (AlSb) is thought to be a potential material for high efficiency solar cells. In this paper, AlSb thin films have been fabricated by DC magnetron sputtering on glass substrates. The sputtering target consists of aluminum and antimony, and the area ratio of Al to Sb is 7:3, which is derived from research into the relationship between the deposition rates of both the metals and sputtering power. XRD and AFM measurements show that the as-deposited films are amorphous, but become polycrystalline with an average grain size of about 20 nm after annealing in an argon atmosphere. From optical absorption measurements of annealed AlSb films, a band gap of 1.56 eV has been demonstrated. Hall measurements show that the films are p-type semiconductors. The temperature dependence of dark conductivity tested in vacuum displays a linear lnσ to 1/T curve, which indicates a conductivity activation energy of around 0.61 eV.
EFFECT OF CELL THICKNESS ON THE DIELECTRIC RELAXATION PROCESSES IN FERROELECTRIC LIQUID CRYSTALS
Authors: SINGH RAJBIR , RAINA K. K.
Published: June 2008

Dielectric relaxation spectroscopy in the frequency range 50 Hz to 1 MHz has been carried out in a room temperature ferroelectric liquid crystal mixture in the SmC*, SmA and N* phases in cells of different thickness. The relaxation frequency fr, distribution parameter α and dielectric strength δ∊ have been evaluated. Goldstone mode, domain mode and soft mode have been observed. It is found that the cell thickness has a significant effect on the dielectric parameters of the ferroelectric liquid crystal material. The results have been discussed.
A NOTE ON THE ANALYSIS OF A HETEROGENEOUS ROD-LIKE CHAIN IN DNA MODELING
Authors: DING YAN , LI TIEJUN
Published: June 2008

Two different results concerning the elastic behavior of the heterogeneous worm-like chain (WLC) [D. Bensimon et al., Europhys. Lett.42, 97 (1998)] and rod-like chain (RLC) [P. Nelson, Phys. Rev. Lett.80, 5810 (1998)] are compared. We argue that the RLC is a more suitable model for double-stranded (ds-) DNA. As the hetero-RLC is the basic model for studying sequence-dependent ds-DNA, a rigorous path integral analysis for the effective bending persistence length is performed in the weak disorder limit. The novelty of the paper is in analyzing a path integral on the Lie group SO(3) with random forcing, which supplies a rigorous basis for the analysis of RLC type models.
THE INFLUENCE OF AN IMPURITY ON PERSISTENT CURRENTS IN CROSSING MESOSCOPIC DOUBLE RINGS
Authors: LI HONG-MING , HUANG YOU-LI , XIAO JING-LIN
Published: June 2008

The transmission probability and the persistent currents in crossing a double-ring system with an impurity are investigated theoretically. The dependence of persistent currents on the sizes of the rings and the influence of the impurity on the transmission and persistent currents are shown. One finds that the impurity potential may help the enhancement of current magnification in a certain range of Fermi energies. Moreover, the persistent currents can be modulated by adjusting the impurity potential.
EFFECT OF IRREGULARITY ON STATIC DEFORMATION OF ELASTIC HALF-SPACE
Authors: SELIM M. M.
Published: June 2008

In the present paper, the problem of two-dimensional static deformation of an isotropic elastic half-space of irregular thickness has been studied using the eigenvalue approach, following a Fourier transform. The irregularity is expressed by a rectangular shape. As an application, the normal line-load acting inside an irregular isotropic half-space has been considered. Further, the results for the displacements have been derived in the closed form. To examine the effect of irregularity, variations of the displacements with horizontal distance have been shown graphically for different values of irregularity size, and they are compared with those for the medium with uniform shape. It is found that irregularity affects the deformation significantly.
SELF-CONTRADICTION AND CONTRADICTION BETWEEN TWO ATANASSOV'S INTUITIONISTIC FUZZY SETS
Authors: CUBILLO SUSANA , TORRES CARMEN , CASTIÑEIRA ELENA
Published: June 2008

The paper focuses on the study of the contradiction between two Atanassov's intuitionistic fuzzy sets. First, taking into account some characterizations obtained in previous papers, some functions are defined in order to measure the degrees of contradiction. Besides the principal properties of these measures are pointed out. Finally, some results relating self-contradiction and contradiction between two Atanassov's intuitionistic fuzzy sets are achieved.
COMBINATION METHODS AND CONFLICT HANDLING IN EVIDENTIAL THEORIES
Authors: MARASHI S. EMAD , DAVIS JOHN P. , HALL JIM W.
Published: June 2008

Evidence theory has been acknowledged as an important approach to dealing with uncertain, incomplete and imperfect information. In this framework, different formal techniques have been developed in order to address information aggregation and conflict handling. The variety of proposed models clearly demonstrates the range of possible underlying assumptions in combination rules. In this paper we present a review of some of the most important methods of combination and conflict handling in order to introduce a more generic rule for aggregation of uncertain evidence. We claim that the models based on mass multiplication can address the problem domains where randomness and stochastic independence is the dominant characteristic of information sources, although these assumptions are not always adhered to many practical cases. The proposed combination rule here is not only capable of retrieving other classical models, but also enables us to define new families of aggregation rules with more flexibility on dependency and normalization assumptions.
LEXICOGRAPHIC METHOD FOR MATRIX GAMES WITH PAYOFFS OF TRIANGULAR FUZZY NUMBERS
Authors: LI DENG-FENG
Published: June 2008

The purpose of the paper is to study how to solve a type of matrix games with payoffs of triangular fuzzy numbers. In this paper, the value of a matrix game with payoffs of triangular fuzzy numbers has been considered as a variable of the triangular fuzzy number. First, based on two auxiliary linear programming models of a classical matrix game and the operations of triangular fuzzy numbers, fuzzy optimization problems are established for two players. Then, based on the order relation of triangular fuzzy numbers the fuzzy optimization problems for players are decomposed into three-objective linear programming models. Finally, using the lexicographic method maximin and minimax strategies for players and the fuzzy value of the matrix game with payoffs of triangular fuzzy numbers can be obtained through solving two corresponding auxiliary linear programming problems, which are easily computed using the existing Simplex method for the linear programming problem. It has been shown that the models proposed in this paper extend the classical matrix game models. A numerical example is provided to illustrate the methodology.
CROSS-LAYER DESIGN FOR MOBILE AD HOC NETWORKS USING INTERVAL TYPE-2 FUZZY LOGIC SYSTEMS
Authors: XIA XINSHENG , LIANG QILIAN
Published: June 2008

In this paper, we introduce a new method for packet transmission delay analysis and prediction in mobile ad hoc networks. We apply a fuzzy logic system (FLS) to coordinate physical layer and data link layer. We demonstrate that type-2 fuzzy membership function (MF), i.e., the Gaussian MFs with uncertain variance is most appropriate to model BER and MAC layer service time. Two FLSs and one neural network: a singleton type-1 FLS, an interval type-2 FLS and back-prop neural network (NN) are designed to predict the packet transmission delay based on the BER and MAC layer service time. Simulation results show that the interval type-2 FLS performs much better than the type-1 FLS in transmission delay prediction. And FLSs performs better than back-prop NN. We use the forecasted transmission delay to adjust the transmission power, and it shows that the interval type-2 FLS performs much better than a type-1 FLS, and FLSs are performs better than back-prop NN in terms of energy consumption, average delay and throughput. Besides, we obtain the performance bound based on the actual transmission delay.
INTERVAL METHODS IN KNOWLEDGE REPRESENTATION
Authors: Kreinovich Vladik
Published: June 2008

This section is maintained by Vladik Kreinovich. Please send your abstracts (or copies of papers that you want to see reviewed here) to vladik@utep.edu, or by regular mail to: V. Kreinovich, Department of Computer Science, University of Texas, El Paso, TX 79968, USA.
Comparison of Mini-Flap Technique and Conjunctival Autograft Transplantation without Mitomycin C in Primary and Recurrent Pterygium
Authors: Kim Min , Chung So Hyang , Lee Jae Hwan , Lee Hyung Keun , Seo Kyoung Yul
Published: June 2008

Aims: Our purpose was to compare postoperative results of pterygium surgery between mini-flap technique and conjunctival autograft transplantation without application of mitomycin C. Methods: This is a retrospective, comparative and observational study. Forty-one eyes underwent conjunctival autograft transplantation without mitomycin C between March 1999 and December 2001 and 49 eyes with pterygium received conjunctival mini-flap without mitomycin C by the same surgeon between January 2002 and February 2004. The main outcome measurement was postoperative recurrence. Results: The recurrence rate in those with primary pterygium was 4.7% (2 of 43) in the mini-flap group and 17.6% (6 of 34) in the conjunctival autograft group. In the patients with recurrent pterygium, recurrence was observed in 1 of 6 cases (16.7%) in the mini-flap group and 1 of 7 cases (14.3%) in the conjunctival autograft group. Overall, the conjunctival mini-flap group without use of mitomycin C had a significantly lower rate of recurrence (6.1%) than the conjunctival autograft transplantation group without mitomycin C (17.1%) (p = 0.042). Conclusion: The mini-flap technique without use of mitomycin C in pterygium surgery is safe and effective in reducing the postoperative recurrence of primary pterygium compared to the conjunctival autograft technique.
Dose Escalation Study of Amrubicin in Combination with Fixed-Dose Irinotecan in Patients with Extensive Small-Cell Lung Cancer
Authors: Oshita Fumihiro , Saito Haruhiro , Yamada Kouzo
Published: June 2008

Background: The combination of amrubicin (Am) and irinotecan (CPT) shows appreciable activity against small-cell lung cancer (SCLC) in vitro. Patients and Methods: We conducted a dose escalation study of Am in combination with CPT to determine the qualitative and quantitative toxicities and efficacy against extensive (ED) SCLC. Results: Thirteen previously untreated patients with ED-SCLC were treated with CPT at 60 mg/m2 on day 1 and dose-escalated Am on days 1–3 with prophylactic granulocyte colony-stimulating factor subcutaneously on days 5–9 every 2–3 weeks. At level 3 (40 mg/m2/day Am), 3 of 4 registered patients experienced dose-limiting toxicity such as grade 4 neutropenic fever, and therefore, this was defined as the maximum tolerated dose. A total of 31 courses was administered at dose level 2 (35 mg/m2/day) in 6 patients, and grade 4 neutropenia was observed during 5 courses (16.1%). Non-hematological toxicities, except 1 course of grade 3 transfusion of red blood cells and 1 course of grade 3 transaminase elevation, were mild. Thus, dose level 2 of Am was recommended for further study. One patient achieved complete remission and 12 achieved partial remission, and the overall response rate was 100%. The median survival time was 17.4 months, and the 1-year survival rate was 76.9%. Conclusions: CPT at 60 mg/m2 on day 1 and Am at 35 mg/m2/day on days 1–3 with granulocyte colony-stimulating factor support every 3 weeks is recommended for Japanese patients with ED-SCLC.
High-Dose Irinotecan plus LV5FU2 or Simplified LV5FU (HD-FOLFIRI) for Patients with Untreated Metastatic Colorectal Cancer: A New Way to Allow Resection of Liver Metastases?
Authors: Ducreux Michel , Raoul Jean-Luc , Marti Pierre , Merrouche Yacine , Tigaud Jean-Marie , Rebischung Christine , Boige Valérie
Published: June 2008

The antitumor efficacy of irinotecan may be dose dependent. This study aimed to determine the safety and efficacy of high-dose (HD) irinotecan combined with LV5FU2 or simplified LV5FU (LV5FUs) in first-line treatment of metastatic colorectal cancer. Patients and Methods: Patients with unresectable and measurable metastatic colorectal cancer, not pretreated for metastatic disease, were given irinotecan 260 mg/m2 combined with LV5FU2 in the first 25 patients, then with LV5FUs (HD-FOLFIRI) in 35 patients. G-CSF was given in case of febrile neutropenia, grade 4 neutropenia >7 days or neutropenia grade >1 at day 15. Results: The response rate was 57% (95% confidence interval 43–69%). Second surgery with curative intent was performed in 28% of patients, leading to 20% radiological complete response. Median response duration, time to progression and overall survival were 11, 9 and 22 months, respectively. The median dose intensity of irinotecan was 117 mg/m2/week. G-CSF was given to 45% of patients over 33% of cycles. Usual toxicity of irinotecan and 5-FU were observed without major increased frequency, except hematological toxicity. Tolerance was similar with LV5FU2 and LV5FUs, though more asymptomatic grade 3–4 neutropenia was observed with LV5FU2. Conclusion: HD-irinotecan plus LV5FU2 or HD-FOLFIRI is feasible and achieved a high response rate and postsurgery complete response rate.
Relationship Between Preventability of Death After Coronary Artery Bypass Graft Surgery and All-Cause Risk-Adjusted Mortality Rates
Authors: Guru Veena , Tu Jack V. , Etchells Edward , Anderson Geoffrey M. , Naylor C. David , Novick Richard J. , Feindel Christopher M. , Rubens Fraser D. , Teoh Kevin , Mathur Avdesh , Hamilton Andrew , Bonneau Daniel , Cutrara Charles , Austin Peter C. , Fremes Stephen E.
Published: June 2008

Background—

The goal of this study was to determine the relationship between all-cause, risk-adjusted, in-hospital mortality after coronary artery bypass graft surgery and the proportion of preventable in-hospital deaths as a measure of quality of care at an institution level.

Methods and Results—

We conducted a retrospective analysis of 347 randomly selected in-hospital deaths after isolated coronary artery bypass graft surgery at 9 institutions in Ontario over the period of 1998 to 2003. Nurse-abstracted chart summaries were reviewed by 2 experienced cardiac surgeons who were blinded to patient, surgeon, and hospital and used a standardized implicit tool to identify preventable death. A third reviewer reassessed all cases in which the first 2 reviewers disagreed. Rates of preventable deaths were estimated for each hospital and compared with all-cause mortality rates. A structured adverse event audit completed by each surgeon-reviewer was used to identify quality improvement opportunities for the preventable deaths. A total of 111 of 347 deaths (32%) were judged preventable despite a low risk-adjusted mortality range (1.3% to 3.1%) across hospitals. No significant correlation was found between all-cause, risk-adjusted in-hospital mortality rates and the proportion of preventable deaths at the hospital level (Spearman coefficient, −0.42;
P
=0.26). A large proportion of preventable deaths were related to problems in the operating room (86%) and intensive care unit (61%). Many deaths were associated with deviations in perioperative care (32% based on concurrence of 2 reviewers, and another 42% in cases in which 1 reviewer reached that opinion).

Conclusions—

Approximately one third of in-hospital coronary artery bypass graft deaths were judged preventable by surgeon reviewers. All-cause risk-adjusted mortality rates are convenient measures of institutional quality of care but were not correlated with preventable mortality in our jurisdiction. Providers should conduct detailed adverse event audits to drive meaningful improvements in quality.
A Theoretical and Numerical Study of Urban Heat Island–Induced Circulation and Convection
Authors: Han Ji-Young , Baik Jong-Jin
Published: June 2008

Urban heat island–induced circulation and convection in three dimensions are investigated theoretically and numerically in the context of the response of a stably stratified uniform flow to specified low-level heating that represents an urban heat island. In a linear, theoretical part of the investigation, an analytic solution for the perturbation vertical velocity in a three-dimensional, time-dependent, hydrostatic, nonrotating, inviscid, Boussinesq airflow system is obtained. The solution reveals a typical internal gravity wave field, including low-level upward motion downwind of the heating center. Precipitation enhancement observed downwind of urban areas may be partly due to this downwind upward motion. The comparison of two- and three-dimensional flow fields indicates that the dispersion of gravity wave energy into an additional dimension results in a faster approach to a quasi-steady state and a weaker quasi-steady flow well above the concentrated heating region in three dimensions.

In a nonlinear, numerical modeling part of the investigation, extensive dry and moist simulations using a nonhydrostatic, compressible model with advanced physical parameterizations [Advanced Regional Prediction System (ARPS)] are performed. While the maximum perturbation vertical velocity in the linear internal gravity wave field exists in the downwind region close to the heating center, the maximum updraft in three-dimensional dry simulations propagates downwind and then becomes quasi stationary. In three-dimensional moist simulations, it is demonstrated that the downwind upward motion induced by an urban heat island can initiate moist convection and result in downwind precipitation. The cloud induced by the downwind upward motion grows rapidly to become deep convective clouds. Heavy rainfalls are localized in a region not far from the heating center by a convective precipitating system that is nearly stationary. The differences in results between two and three dimensions are explained by the presence of (moist) convergence in an additional dimension. The numerical simulation results indicate that the intensity and horizontal structure of the urban heat island affect those of circulation and convection and hence the distribution of surface precipitation.
The Geometry of Model Error
Authors: Judd Kevin , Reynolds Carolyn A. , Rosmond Thomas E. , Smith Leonard A.
Published: June 2008

This paper investigates the nature of model error in complex deterministic nonlinear systems such as weather forecasting models. Forecasting systems incorporate two components, a forecast model and a data assimilation method. The latter projects a collection of observations of reality into a model state. Key features of model error can be understood in terms of geometric properties of the data projection and a model attracting manifold. Model error can be resolved into two components: a projection error, which can be understood as the model’s attractor being in the wrong location given the data projection, and direction error, which can be understood as the trajectories of the model moving in the wrong direction compared to the projection of reality into model space. This investigation introduces some new tools and concepts, including the shadowing filter, causal and noncausal shadow analyses, and various geometric diagnostics. Various properties of forecast errors and model errors are described with reference to low-dimensional systems, like Lorenz’s equations; then, an operational weather forecasting system is shown to have the same predicted behavior. The concepts and tools introduced show promise for the diagnosis of model error and the improvement of ensemble forecasting systems.
Abrupt Seasonal Migration of the ITCZ into the Summer Hemisphere
Authors: Xian Peng , Miller Ron L.
Published: June 2008

Although the maximum of solar radiation at the top of the atmosphere moves gradually from one hemisphere to the other as part of the seasonal cycle, the intertropical convergence zone (ITCZ) moves abruptly into the summer hemisphere. An axisymmetric circulation model is developed to study this rapid transition. The model consists of an upper and lower layer of the Hadley circulation (HC), with the surface layer attached to a slab ocean and the lower layer connected to the upper layer by a constant lapse rate. The model is forced by solar heating, and the ITCZ is prescribed to coincide with the warmest sea surface temperature (SST). The collocation of tropical rainfall with warm SST allows the model ITCZ migration to be understood in terms of the relative influence of solar heating and atmospheric dynamics upon ocean temperature. Atmospheric dynamics allow the ITCZ to move off the equator by flattening the meridional temperature gradient that would exist in radiative–convective equilibrium. For the present-day tropical oceanic mixed layer depth and ITCZ width, the model exhibits an abrupt seasonal transition of the ITCZ across the equator. It is found that there are two determinative factors on the abrupt transition of the ITCZ: the nonlinear meridional advection of angular momentum by the circulation and ocean thermal inertia. As a result of nonlinear dynamics, angular momentum is well mixed, resulting in minimum atmospheric temperature at the equator and a similar equatorial minimum in SST. This inhibits convection over the equator while favoring a rapid seasonal transition of the ITCZ between the warmer surface water on either side of this latitude.
Sensitivity of a Large Ensemble of Tropical Convective Systems to Changes in the Thermodynamic and Dynamic Forcings
Authors: Eitzen Zachary A. , Xu Kuan-Man
Published: June 2008

A two-dimensional cloud-resolving model (CRM) is used to perform five sets of simulations of 68 deep convective cloud objects identified with Clouds and the Earth’s Radiant Energy System (CERES) data to examine their sensitivity to changes in thermodynamic and dynamic forcings. The control set of simulations uses observed sea surface temperatures (SSTs) and is forced by advective cooling and moistening tendencies derived from a large-scale model analysis matched to the time and location of each cloud object. Cloud properties, such as albedo, effective cloud height, cloud ice and snow path, and cloud radiative forcing (CRF), are analyzed in terms of their frequency distributions rather than their mean values.

Two sets of simulations, F+50% and F−50%, use advective tendencies that are 50% greater and 50% smaller than the control tendencies, respectively. The increased cooling and moistening tendencies cause more widespread convection in the F+50% set of simulations, resulting in clouds that are optically thicker and higher than those produced by the control and F−50% sets of simulations. The magnitudes of both longwave and shortwave CRF are skewed toward higher values with the increase in advective forcing. These significant changes in overall cloud properties are associated with a substantial increase in deep convective cloud fraction (from 0.13 for the F−50% simulations to 0.34 for the F+50% simulations) and changes in the properties of non–deep convective clouds, rather than with changes in the properties of deep convective clouds.

Two other sets of simulations, SST+2K and SST−2K, use SSTs that are 2 K higher and 2 K lower than those observed, respectively. The updrafts in the SST+2K simulations tend to be slightly stronger than those of the control and SST−2K simulations, which may cause the SST+2K cloud tops to be higher. The changes in cloud properties, though smaller than those due to changes in the dynamic forcings, occur in both deep convective and non–deep convective cloud categories. The overall changes in some cloud properties are moderately significant when the SST is changed by 4 K. The changes in the domain-averaged shortwave and longwave CRFs are larger in the dynamic forcing sensitivity sets than in the SST sensitivity sets. The cloud feedback effects estimated from the SST−2K and SST+2K sets are comparable to prior studies.
Shortwave Radiative Impacts from Aerosol Effects on Marine Shallow Cumuli
Authors: Zuidema Paquita , Xue Huiwen , Feingold Graham
Published: June 2008

The net shortwave radiative impact of aerosol on simulations of two shallow marine cloud cases is investigated using a Monte Carlo radiative transfer model. For a shallow cumulus case, increased aerosol concentrations are associated not only with smaller droplet sizes but also reduced cloud fractions and cloud dimensions, a result of evaporation-induced mixing and a lack of precipitation. Three-dimensional radiative transfer (3DRT) effects alter the fluxes by 10%–20% from values calculated using the independent column approximation for these simulations. The first (Twomey) aerosol indirect effect is dominant but the decreased cloud fraction reduces the magnitude of the shortwave cloud forcing substantially. The 3DRT effects slightly decrease the sensitivity of the cloud albedo to changes in droplet size under an overhead sun for the two ranges of cloud liquid water paths examined, but not strongly so. A popular two-stream radiative transfer approximation to the cloud susceptibility overestimates the more directly calculated values for the low liquid-water-path clouds within pristine aerosol conditions by a factor of 2 despite performing well otherwise, suggesting caution in its application to the cloud albedos within broken cloud fields. An evaluation of the influence of cloud susceptibility and cloud fraction changes to a “domain” area-weighted cloud susceptibility found that the domain cloud albedo is more likely to increase under aerosol loading at intermediate aerosol concentrations than under the most pristine conditions, contrary to traditional expectations.

The second simulation (cumulus penetrating into stratus) is characterized by higher cloud fractions and more precipitation. This case has two regimes: a clean, precipitating regime where cloud fraction increases with increasing aerosol, and a more polluted regime where cloud fraction decreases with increasing aerosol. For this case the domain-mean cloud albedo increases steadily with aerosol loading under clean conditions, but increases only slightly after the cloud coverage decreases. Three-dimensional radiative transfer effects are mostly negligible for this case. Both sets of simulations suggest that aerosol-induced cloud fraction changes must be considered in tandem with the Twomey effect for clouds of small dimensions when assessing the net radiative impact, because both effects are drop size dependent and radiatively significant.
Modeling of the Melting Layer. Part IV: Brightband Bulk Parameterization
Authors: Heyraud Catherine , Szyrmer Wanda , Laroche Stéphane , Zawadzki Isztar
Published: June 2008

In this paper a simplified UHF-band backscattering parameterization for individual melting snowflakes is proposed. This parameterization is a function of the density, shape, and melted fraction, and is used here in a brightband bulk modeling study. A 1D bulk model is developed where aggregation and breakup are neglected. Model results are in good agreement with detailed bin-model results and simulate the radar brightband observations well. It is shown the model can be seen as an observation operator that could be introduced into a data assimilation scheme to extract information contained in the radar data measurements.
Vertically Propagating Kelvin Waves and Tropical Tropopause Variability
Authors: Ryu Jung-Hee , Lee Sukyoung , Son Seok-Woo
Published: June 2008

The relationship between local convection, vertically propagating Kelvin waves, and tropical tropopause height variability is examined. This study utilizes both simulations of a global primitive-equation model and global observational datasets. Regression analysis with the data shows that convection over the western tropical Pacific is followed by warming in the upper troposphere (UT) and cooling in lower stratosphere (LS) over most longitudes, which results in a lifting of the tropical tropopause. The model results reveal that these UT–LS temperature anomalies are closely associated with vertically propagating Kelvin waves, indicating that these Kelvin waves drive tropical tropopause undulations at intraseasonal time scales.

The model simulations further show that regardless of the longitudinal position of the imposed heating, the UT–LS Kelvin wave reaches its maximum amplitude over the western Pacific. This result, together with an analysis based on wave action conservation, is used to contend that the Kelvin wave amplification over the western Pacific should be attributed to the zonal variation of background zonal wind field, rather than to the proximity of the heating. The wave action conservation law is also used to offer an explanation as to why the vertically propagating Kelvin waves play the central role in driving tropical tropopause height undulations.

The zonal and vertical modulation of the Kelvin waves by the background flow may help explain the origin of the very cold air over the western tropical Pacific, which is known to cause freeze-drying of tropospheric air en route to the stratosphere.
Statistics of an Unstable Barotropic Jet from a Cumulant Expansion
Authors: Marston J. B. , Conover E. , Schneider Tapio
Published: June 2008

Low-order equal-time statistics of a barotropic flow on a rotating sphere are investigated. The flow is driven by linear relaxation toward an unstable zonal jet. For relatively short relaxation times, the flow is dominated by critical-layer waves. For sufficiently long relaxation times, the flow is turbulent. Statistics obtained from a second-order cumulant expansion are compared to those accumulated in direct numerical simulations, revealing the strengths and limitations of the expansion for different relaxation times.
Small-Scale Moist Turbulence in Numerically Generated Convective Clouds
Authors: Spyksma K. , Bartello P.
Published: June 2008

The authors present simulations of cloud-free and cloudy, nonprecipitating, convective turbulence at spatial resolutions down to Δx = 2.6 m for a domain size of (1 km)3. The runs are analyzed with attention focused on the dynamical differences between resolutions and the presence or absence of moisture, as well as on the small-scale variability of the liquid water spectra in the cloudy cases. Because of evaporation and condensation, liquid water content does not act like a passive scalar. Much of the evaporation occurs in highly turbulent cloud-top mixing where differences in variances and kurtoses of real-space vorticity probability density functions between cloudy and cloud-free runs are also found. The cloudy cases have higher variance and lower kurtosis values than their cloud-free counterparts. The lower kurtosis values mean fewer high-intensity vortices for the cloudy cases, which is most likely due to the loss of buoyancy as evaporation occurs during entrainment events. This effect is associated with a change in the liquid water content spectra found in regions of cloud decay. Conditional sampling of these regions shows increased small-scale variability, above the background increase due to the bottleneck effect, of liquid water content spectra; this is not found in other cloudy regions. This may help explain recent measurements of enhanced small-scale liquid water content variability in aircraft measurements of stratocumulus clouds.
Factors Determining the Impact of Aerosols on Surface Precipitation from Clouds: An Attempt at Classification
Authors: Khain A. P. , BenMoshe N. , Pokrovsky A.
Published: June 2008

The simulation of the dynamics and the microphysics of clouds observed during the Large-Scale Biosphere–Atmosphere Experiment in Amazonia—Smoke, Aerosols, Clouds, Rainfall, and Climate (LBA–SMOCC) campaign, as well as extremely continental and extremely maritime clouds, is performed using an updated version of the Hebrew University spectral microphysics cloud model (HUCM). A new scheme of diffusional growth allows the reproduction of in situ–measured droplet size distributions including those formed in extremely polluted air. It was shown that pyroclouds forming over the forest fires can precipitate. Several mechanisms leading to formation of precipitation from pyroclouds are considered.

The mechanisms by which aerosols affect the microphysics and precipitation of warm cloud-base clouds have been investigated by analyzing the mass, heat, and moisture budgets. The increase in aerosol concentration increases both the generation and the loss of the condensate mass. In the clouds developing in dry air, the increase in the loss is dominant, which suggests a decrease in the accumulated precipitation with the aerosol concentration increase. On the contrary, an increase in aerosol concentration in deep maritime clouds leads to an increase in precipitation. The precipitation efficiency of clouds in polluted air is found to be several times lower than that of clouds forming in clean air. A classification of the results of aerosol effects on precipitation from clouds of different types developing in the atmosphere with high freezing level (about 4 km) is proposed. The role of air humidity and other factors in precipitation’s response to aerosols is discussed. The analysis shows that many discrepancies between the results reported in different observational and numerical studies can be attributed to the different atmospheric conditions and cloud types analyzed.
A Warm Rain Microphysics Parameterization that Includes the Effect of Turbulence
Authors: Franklin Charmaine N.
Published: June 2008

A warm rain parameterization has been developed by solving the stochastic collection equation with the use of turbulent collision kernels. The resulting parameterizations for the processes of autoconversion, accretion, and self-collection are functions of the turbulent intensity of the flow and are applicable to turbulent cloud conditions ranging in dissipation rates of turbulent kinetic energy from 100 to 1500 cm2 s−3. Turbulence has a significant effect on the acceleration of the drop size distribution and can reduce the time to the formation of raindrops. When the stochastic collection equation is solved with the gravitational collision kernel for an initial distribution with a liquid water content of 1 g m−3 and 240 drops cm−3 with a mean volume radius of 10 μm, the amount of mass that is transferred to drop sizes greater than 40 μm in radius after 20 min is 0.9% of the total mass. When the stochastic collection equation is solved with a turbulent collision kernel for collector drops in the range of 10–30 μm with a dissipation rate of turbulent kinetic energy equal to 100 cm2 s−3, this percentage increases to 21.4. Increasing the dissipation rate of turbulent kinetic energy to 500, 1000, and 1500 cm2 s−3 further increases the percentage of mass transferred to radii greater than 40 μm after 20 min to 41%, 52%, and 58%, respectively, showing a substantial acceleration of the drop size distribution when a turbulent collision kernel that includes both turbulent and gravitational forcing replaces the purely gravitational kernel. The warm rain microphysics parameterization has been developed from direct numerical simulation (DNS) results that are characterized by Reynolds numbers that are orders of magnitude smaller than those of atmospheric turbulence. The uncertainty involved with the extrapolation of the results to high Reynolds numbers, the use of gravitational collision efficiencies, and the range of the droplets for which the effect of turbulence has been included should all be considered when interpreting results based on these new microphysics parameterizations.
Piecewise Potential Vorticity Inversion: Elementary Tests
Authors: Egger Joseph
Published: June 2008

Piecewise potential vorticity inversion (PPVI) is widely accepted as a useful tool in atmospheric diagnostics. This method is thought to quantify the instantaneous interaction at a distance of anomalies of potential vorticity (PV) separated horizontally and/or vertically. Doubts with respect to the dynamical justification of PPVI are formulated. In particular, it is argued that the tendency of the inverted streamfunction must be determined in order to quantify far-field effects. Elementary tests of PPVI are conducted to clarify these points. First, PPVI is performed for the textbook case of linear Rossby waves in a one-dimensional barotropic fluid. Analytic solutions are presented for PPVI and the related tendency problem. It is found that PPVI does not contribute to an understanding of Rossby wave dynamics. On the other hand, PPVI turns out to be more useful when applied to confined PV extrema. Neither the application of PPVI to linear baroclinic waves in zonal shear flow nor the inversions of the related temperature anomalies at the boundaries help to better understand the wave development.

It is concluded that PPVI with additional tendency calculations poses and solves a specific problem by retaining observed PV anomalies in one subdomain and removing them in others. The usefulness of the results with regard to the diagnosis of the observed state depends strongly on the flows considered and on the partitions chosen, which must comply with a simple rule.
Mountain Waves in Two-Layer Sheared Flows: Critical-Level Effects, Wave Reflection, and Drag Enhancement
Authors: Teixeira Miguel A. C. , Miranda Pedro M. A. , Argaín JoséL.
Published: June 2008

Internal gravity waves generated in two-layer stratified shear flows over mountains are investigated here using linear theory and numerical simulations. The impact on the gravity wave drag of wind profiles with constant unidirectional or directional shear up to a certain height and zero shear above, with and without critical levels, is evaluated. This kind of wind profile, which is more realistic than the constant shear extending indefinitely assumed in many analytical studies, leads to important modifications in the drag behavior due to wave reflection at the shear discontinuity and wave filtering by critical levels. In inviscid, nonrotating, and hydrostatic conditions, linear theory predicts that the drag behaves asymmetrically for backward and forward shear flows. These differences primarily depend on the fraction of wavenumbers that pass through their critical level before they are reflected by the shear discontinuity. If this fraction is large, the drag variation is not too different from that predicted for an unbounded shear layer, while if it is small the differences are marked, with the drag being enhanced by a considerable factor at low Richardson numbers (Ri). The drag may be further enhanced by nonlinear processes, but its qualitative variation for relatively low Ri is essentially unchanged. However, nonlinear processes seem to interact constructively with shear, so that the drag for a noninfinite but relatively high Ri is considerably larger than the drag without any shear at all.
Symmetric Stability of Compressible Zonal Flows on a Generalized Equatorial β Plane
Authors: Fruman Mark D. , Shepherd Theodore G.
Published: June 2008

Sufficient conditions are derived for the linear stability with respect to zonally symmetric perturbations of a steady zonal solution to the nonhydrostatic compressible Euler equations on an equatorial β plane, including a leading order representation of the Coriolis force terms due to the poleward component of the planetary rotation vector.

A version of the energy–Casimir method of stability proof is applied: an invariant functional of the Euler equations linearized about the equilibrium zonal flow is found, and positive definiteness of the functional is shown to imply linear stability of the equilibrium. It is shown that an equilibrium is stable if the potential vorticity has the same sign as latitude and the Rayleigh centrifugal stability condition that absolute angular momentum increase toward the equator on surfaces of constant pressure is satisfied. The result generalizes earlier results for hydrostatic and incompressible systems and for systems that do not account for the nontraditional Coriolis force terms.

The stability of particular equilibrium zonal velocity, entropy, and density fields is assessed. A notable case in which the effect of the nontraditional Coriolis force is decisive is the instability of an angular momentum profile that decreases away from the equator but is flatter than quadratic in latitude, despite its satisfying both the centrifugal and convective stability conditions.
On Simultaneous Data-Based Dimension Reduction and Hidden Phase Identification
Authors: Horenko Illia
Published: June 2008

A problem of simultaneous dimension reduction and identification of hidden attractive manifolds in multidimensional data with noise is considered. The problem is approached in two consecutive steps: (i) embedding the original data in a sufficiently high-dimensional extended space in a way proposed by Takens in his embedding theorem, followed by (ii) a minimization of the residual functional. The residual functional is constructed to measure the distance between the original data in extended space and their reconstruction based on a low-dimensional description. The reduced representation of the analyzed data results from projection onto a fixed number of unknown low-dimensional manifolds. Two specific forms of the residual functional are proposed, defining two different types of essential coordinates: (i) localized essential orthogonal functions (EOFs) and (ii) localized functions called principal original components (POCs). The application of the framework is exemplified both on a Lorenz attractor model with measurement noise and on historical air temperature data. It is demonstrated how the new method can be used for the elimination of noise and identification of the seasonal low-frequency components in meteorological data. An application of the proposed POCs in the context of the low-dimensional predictive models construction is presented.
Horizontally Homogeneous Rotating Radiative–Convective Equilibria at GCM Resolution
Authors: Held Isaac M. , Zhao Ming
Published: June 2008

Rotating radiative–convective equilibrium, using the column physics and resolution of GCMs, is proposed as a useful framework for studying the tropical storm–like vortices produced by global models. These equilibria are illustrated using the column physics and dynamics of a version of the GFDL Atmospheric Model 2 (AM2) at resolutions of 220, 110, and 55 km in a large 2 × 104 km square horizontally homogeneous domain with fixed sea surface temperature and uniform Coriolis parameter. The large domain allows a number of tropical storms to exist simultaneously. Once equilibrium is attained, storms often persist for hundreds of days. The number of storms decreases as sea surface temperatures increase, while the average intensity increases. As the background rotation is decreased, the number of storms also decreases. At these resolutions and with this parameterization of convection, a dense collection of tropical storms is always the end state of moist convection in the cases examined.
L-Moment Estimators as Applied to Gamma Drop Size Distributions
Authors: Kliche Donna V. , Smith Paul L. , Johnson Roger W.
Published: June 2008

The traditional approach with experimental raindrop size data has been to use the method of moments in the fitting procedure to estimate the parameters for the raindrop size distribution function. However, the moment method is known to be biased and can have substantial errors. Therefore, the L-moment method, which is widely used by hydrologists, was investigated as an alternative. The L-moment method was applied, along with the moment and maximum likelihood methods, to samples taken from simulated gamma raindrop populations. A comparison of the bias and the errors involved in the L-moments, moments, and maximum likelihood procedures shows that, with samples covering the full range of drop sizes, L-moments and maximum likelihood outperform the method of moments. For small sample sizes the moment method gives a large bias and large error while the L-moment method gives results close to the true population values, outperforming even maximum likelihood results. Because the goal of this work is to understand the properties of the various fitting procedures, the investigation was expanded to include the effects of the absence of small drops in the samples (typical disdrometer minimum size thresholds are 0.3–0.5 mm). The results show that missing small drops (due to the instrumental constraint) can result in a large bias in the case of the L-moment and maximum likelihood fitting methods; this bias does not decrease much with increasing sample size. Because the very small drops have a negligible contribution to moments of order 2 or higher, the bias in the moment methods seems to be about the same as in the case of full samples. However, when moments of order less than 2 are needed (as in the case of modelers using moments 0 and 3), the moment method gives much larger bias. Therefore a modification of these methods is needed to handle the truncated-data situation.