bluuebunny/crossref_metadata_2025 huggingface dataset:
JB*-Algebras of Topological Stable Rank 1
Authors: Siddiqui Akhlaq A.
Published: April 2007

In 1976, Kaplansky introduced the classJB*-algebras which includes allC*-algebras as a proper subclass. The notion of topological stable rank 1 forC*-algebras was originally introduced by M. A. Rieffel and was extensively studied by various authors. In this paper, we extend this notion to generalJB*-algebras. We show that the complex spin factors are of tsr 1 providing an example of specialJBW*-algebras for which the enveloping von Neumann algebras may not be of tsr 1. In the sequel, we prove that every invertible element of aJB*-algebra𝒥is positive in certain isotope of𝒥; if the algebra is finite-dimensional, then it is of tsr 1 and every element of𝒥is positive in some unitary isotope of𝒥. Further, it is established that extreme points of the unit ball sufficiently close to invertible elements in aJB*-algebra must be unitaries and that in anyJB*-algebras of tsr 1, all extreme points of the unit ball are unitaries. In the end, we prove the coincidence between theλ-function andλu-function on invertibles in aJB*-algebra.
Plastic Deformation Instabilities: Lambert Solutions of Mecking-Lücke Equation with Delay
Authors: Hilout Saïd , Boutat Mohammed , Grilhé Jean
Published: April 2007

The aim of this paper is the study of instabilities during plastic deformation at constant cross‐head velocity. The deformation is supposed to be controlled by the emission of dislocation loops. Under some hypothesis analogous to the Mecking‐Lücke relation, we derive a linear delay differential‐difference equation. The “retarded” time term appears as the phase shift between the time of loop nucleation and the time at which the mean strain is recorded. We show the existence of the solution of strain equation. We give an analytic approach of solution using Lambert functions. The stability is also investigated close to the stable solution using a linearization of the number of nucleated loops functions.
Nonderogatory Unicyclic Digraphs
Authors: Bravo Diego , Rada Juan
Published: April 2007

A digraph is nonderogatory if its characteristic polynomial and minimal polynomial are equal. We find a characterization of nonderogatory unicyclic digraphs in terms of Hamiltonicity conditions. An immediate consequence of this characterization ia that the complete product of difans and diwheels is nonderogatory.
Existence and Orbital Stability of Cnoidal Waves for a 1D Boussinesq Equation
Authors: Angulo Jaime , Quintero Jose R.
Published: April 2007

We will study the existence and stability of periodic travelling-wave solutions of the nonlinear one-dimensional Boussinesq-type equationΦtt−Φxx+aΦxxxx−bΦxxtt+ΦtΦxx+2ΦxΦxt=0. Periodic travelling-wave solutions with an arbitrary fundamental periodT0will be built by using Jacobian elliptic functions. Stability (orbital) of these solutions by periodic disturbances with periodT0will be a consequence of the general stability criteria given by M. Grillakis, J. Shatah, and W. Strauss. A complete study of the periodic eigenvalue problem associated to the Lame equation is set up.
A Heuristic Approach for Determining Lot Sizes and Schedules Using Power-of-Two Policy
Authors: Ekinci Esra , Ornek Arslan M.
Published: April 2007

We consider the problem of determining realistic and easy-to-schedule lot sizes in a multiproduct, multistage manufacturing environment. We concentrate on a specific type of production, namely, flow shop type production. The model developed consists of two parts, lot sizing problem and scheduling problem. In lot sizing problem, we employ binary integer programming and determine reorder intervals for each product using power-of-two policy. In the second part, using the results obtained of the lot sizing problem, we employ mixed integer programming to determine schedules for a multiproduct, multistage case with multiple machines in each stage. Finally, we provide a numerical example and compare the results with similar methods found in practice.
Suboptimal RED Feedback Control for Buffered TCP Flow Dynamics in Computer Network
Authors: Ahmed N. U. , Ouyang X. H.
Published: April 2007

We present an improved dynamic system that simulates the behavior of TCP flows and active queue management (AQM) system. This system can be modeled by a set of stochastic differential equations driven by a doubly stochastic point process with intensities being the controls. The feedback laws proposed monitor the status of buffers and multiplexor of the router, detect incipient congestion by sending warning signals to the sources. The simulation results show that the optimal feedback control law from the class of linear as well as quadratic polynomials can improve the system performance significantly in terms of maximizing the link utilization, minimizing congestion, packet losses, as well as global synchronization. The optimization process used is based on random recursive search technique known as RRS.
Field-Weakening Nonlinear Control of a Separately Excited DC Motor
Authors: Zribi Mohamed , Al-Zamel Adel
Published: April 2007

This paper investigates the design and implementation of nonlinear control schemes for a separately excited DC motor operating in the field-weakening region. A feedback linearization controller, a Corless-Leitman-type controller, and two nonlinear controllers are designed and implemented for a DC motor system. The stability of the closed-loop system is proved using Lyapunov theory. A hardware testbed is constructed to experimentally verify the designed controllers. The hardware consists of a DC motor system, a DSP controller board, a power module, two current sensors, and a tachogenerator. The experimental results indicate that the developed controllers work well.
Size-Selected SnO1.8: Ag Mixed Nanoparticle Films for Ethanol, CO, and CH4Detection
Authors: Joshi Rakesh Kumar , Kruis Frank Einar
Published: April 2007

Mixed nanoparticle films of SnO1.8: Ag prepared by the gas phase condensation method using an aerosol route have been used for the detection of CO and CH4. Particle size as estimated by transmission electron microscopy is 20 nm for both SnO1.8and Ag nanoparticles. The gas-sensing behavior of the films for these gases has been studied in detail as a function of Ag concentration in the films. A study has been made in order to distinguish the size effect and specific surface area effect in the ethanol gas-sensing behavior of SnO1.8: Ag mixed nanoparticle films. This distinction, which has not been possible using the traditional methods of the sensor fabrication, gives evidence of the dominance of size effect of the metal dopant over the surface area effect in the gas sensing of the films. The sensors show also an increased sensor signal with increase of Ag concentration in the films for CO and CH4. It is observed from the comparative study of the sensing behavior of SnO1.8: Ag films for CO and CH4that the sensors are more sensitive towards CO as compared to CH4. The mixed nanoparticle films were also used for the detection of CO at 100 ppm level.
Oscillatority Conditions for Nonlinear Systems with Delay
Authors: Efimov Denis V. , Fradkov Alexander L.
Published: April 2007

Sufficient conditions for oscillatority in the sense of Yakubovich for a class of time delay nonlinear systems are proposed. Under proposed conditions, upper and lower bounds for oscillation amplitude are given. Examples illustrating analytical results by computer simulation are presented.
Fault Detection and Control of Process Systems
Authors: Minh Vu Trieu , Afzulpurkar Nitin , Wan Muhamad W. M.
Published: April 2007

This paper develops a stochastic hybrid model-based control system that can determine online the optimal control actions, detect faults quickly in the control process, and reconfigure the controller accordingly using interacting multiple-model (IMM) estimator and generalized predictive control (GPC) algorithm. A fault detection and control system consists of two main parts: the first is the fault detector and the second is the controller reconfiguration. This work deals with three main challenging issues: design of fault model set, estimation of stochastic hybrid multiple models, and stochastic model predictive control of hybrid multiple models. For the first issue, we propose a simple scheme for designing faults for discrete and continuous random variables. For the second issue, we consider and select a fast and reliable fault detection system applied to the stochastic hybrid system. Finally, we develop a stochastic GPC algorithm for hybrid multiple-models controller reconfiguration with soft switching signals based on weighted probabilities. Simulations for the proposed system are illustrated and analyzed.
Differential MR/GR Activation in Mice Results in Emotional States Beneficial or Impairing for Cognition
Authors: Brinks Vera , van der Mark Maaike H. , de Kloet E. Ron , Oitzl Melly S.
Published: April 2007

Corticosteroids regulate stress response and influence emotion, learning, and memory via two receptors in the brain, the high‐affinity mineralocorticoid (MR) and low‐affinity glucocorticoid receptor (GR). We test the hypothesis that MR- and GR-mediated effects interact in emotion and cognition when a novel situation is encountered that is relevant for a learning process. By adrenalectomy and additional constant corticosterone supplement we obtained four groups of male C57BL/6J mice with differential chronic MR and GR activations. Using a hole board task, we found that mice with continuous predominant MR and moderate GR activations were fast learners that displayed low anxiety and arousal together with high directed explorative behavior. Progressive corticosterone concentrations with predominant action via GR induced strong emotional arousal at the expense of cognitive performance. These findings underline the importance of a balanced MR/GR system for emotional and cognitive functioning that is critical for mental health.
Inhibitory Effect of Inflexinol on Nitric Oxide Generation and iNOS Expression via Inhibition of NF-κBActivation
Authors: Lee Jae Woong , Lee Moon Soon , Kim Tae Hun , Lee Hwa Jeong , Hong Seong Su , Noh Young Hee , Hwang Bang Yeon , Ro Jai Seup , Hong Jin Tae
Published: April 2007

Inflexinol, anent-kaurane diterpenoid, was isolated from the leaves ofIsodon excisus. Many diterpenoids isolated from the genusIsodon(Labiatae) have antitumor and antiinflammatory activities. We investigated the antiinflammatory effect of inflexinol in RAW 264.7 cells and astrocytes. As a result, we found that inflexinol (1, 5, 10μM) suppressed the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) as well as the production of nitric oxide (NO) in LPS-stimulated RAW 264.7 cells and astrocytes. Consistent with the inhibitory effect on iNOS and COX-2 expression, inflexinol also inhibited transcriptional and DNA binding activity of NF-κBvia inhibition ofIκBdegradation as well as p50 and p65 translocation into nucleus. These results suggest that inflexinol inhibits iNOS and COX-2 expression through inhibition of NF-κBactivation, thereby inhibits generation of inflammatory mediators in RAW 264.7 cells and astrocytes, and may be useful for treatment of inflammatory diseases.
Activated Pregnenolone X-Receptor Is a Target for Ketoconazole and Its Analogs
Authors: Wang Hongwei , Huang Haiyan , Li Hao , Teotico Denise G. , Sinz Michael , Baker Sharyn D. , Staudinger Jeffrey , Kalpana Ganjam , Redinbo Matthew R. , Mani Sridhar
Published: April 2007

Purpose: Variations in biotransformation and elimination of microtubule-binding drugs are a major cause of unpredictable side effects during cancer therapy. Because the orphan receptor, pregnenolone X-receptor (PXR), coordinately regulates the expression of paclitaxel metabolizing and transport enzymes, controlling this process could improve therapeutic outcome.

Experimental Design: In vitro RNA-, protein-, and transcription-based assays in multiple cell lines derived from hepatocytes and PXR wild-type and null mouse studies were employed to show the effects of ketoconazole and its analogues on ligand-activated PXR-mediated gene transcription and translation.

Results: The transcriptional activation of genes regulating biotransformation and transport by the liganded human nuclear xenobiotic receptor, PXR, was inhibited by the commonly used antifungal ketoconazole and related azole analogs. Mutations at the AF-2 surface of the human PXR ligand-binding domain indicate that ketoconazole may interact with specific residues outside the ligand-binding pocket. Furthermore, in contrast to that observed in PXR (+/+) mice, genetic loss of PXR results in increased (preserved) blood levels of paclitaxel.

Conclusions: These studies show that some azole compounds repress the coordinated activation of genes involved in drug metabolism by blocking PXR activation. Because loss of PXR maintains blood levels of paclitaxel upon chronic dosing, ketoconazole analogues may also serve to preserve paclitaxel blood levels on chronic dosing of drugs. Our observations may facilitate new strategies to improve the clinical efficacy of drugs and to reduce therapeutic side effects.
Serum Cytokine Profiling as a Diagnostic and Prognostic Tool in Ovarian Cancer: A Potential Role for Interleukin 7
Authors: Lambeck Annechien J.A. , Crijns Anne P.G. , Leffers Ninke , Sluiter Wim J. , ten Hoor Klaske A. , Braid Mike , van der Zee Ate G.J. , Daemen Toos , Nijman Hans W. , Kast W. Martin
Published: April 2007

Purpose: To evaluate if serum cytokine levels could be used as diagnostic or prognostic markers in ovarian cancer.

Experimental Design: A cytokine bead array was done to simultaneously analyze 14 cytokines in the sera of 187 ovarian cancer patients with complete clinicopathologic data and follow-up, 45 patients with benign ovarian tumors, and 50 healthy controls. Serum levels of the well-known serum tumor marker CA-125 were routinely measured in all patients.

Results: Serum levels of CA-125, interleukin 6 (IL-6), IL-7, and IL-10 were elevated in ovarian cancer patients compared with patients with benign ovarian tumors. Analyzing the cytokines in combination with CA-125 showed that a combination of IL-7 and CA-125 serum levels could accurately predict 69% of the ovarian cancer patients, without falsely classifying patients with benign pelvic mass. The cytokines IL-6, IL-7, IL-8, IL-10, monocyte chemotactic protein-1 (MCP-1), and IP-10 and CA-125 were associated with disease-free and overall survival in univariate analysis. In multivariate analysis, IL-7 and IP-10 were independent predictors of overall survival, although after inclusion of the clininopathologic parameters, only stage and residual disease remained as independent predictors of survival.

Conclusions: IL-7 levels were found to be strongly associated with ovarian cancer and could be used in combination with CA-125 to distinguish between malignant and benign ovarian tumors.
Systemic Interleukin-2 and Adoptive Transfer of Lymphokine-Activated Killer Cells Improves Antibody-Dependent Cellular Cytotoxicity in Patients with Relapsed B-Cell Lymphoma Treated with Rituximab
Authors: Berdeja Jesús G. , Hess Allan , Lucas David M. , O'Donnell Paul , Ambinder Richard F. , Diehl Louis F. , Carter-Brookins Denise , Newton Susan , Flinn Ian W.
Published: April 2007

Purpose: Murine models have shown that antibody-dependent cellular cytotoxicity (ADCC) can be improved with addition of lymphokine-activated killer (LAK) cells to monoclonal antibodies. A pilot trial of rituximab and LAK cells in patients with rituximab-refractory CD20+ lymphoma was conducted to evaluate this approach.

Experimental Design: Ten patients received 3 million units/m2 of interleukin-2 (IL-2) i.v. qd on days 1 to 5 and leukapheresed on days 8, 9, and 10. The leukapheresis product was cultured with IL-2 for 48 h to produce LAK cells. Patients then received 375 mg/m2 i.v. rituximab and LAK cells on days 10, 11, and 12. The patients also received 3 million units/m2 of IL-2 i.v. for 5 days starting day 10. For safety purposes, the first three patients did not receive any LAK cell infusions.

Results: The LAK cell infusions improved the ADCC activity of peripheral blood lymphocytes compared with pretreatment activity and prevented the decline in ADCC seen after infusion of rituximab alone. Therapy was well tolerated and the most clinically significant toxicities were fever and fatigue. Two patients achieved a partial remission and five had stable disease.

Conclusions: The results from these studies suggest that the addition of LAK cells to rituximab augments ADCC in patients with rituximab-refractory lymphoma.
In vivoImaging of Oral Mucositis in an Animal Model Using Optical Coherence Tomography and Optical Doppler Tomography
Authors: Wilder-Smith Petra , Hammer-Wilson Marie J. , Zhang Jun , Wang Qiang , Osann Kathryn , Chen Zhongping , Wigdor Harvey , Schwartz Joel , Epstein Joel
Published: April 2007

Purpose: To assess noninvasive optical coherence tomography (OCT) and optical Doppler tomography (ODT) for early detection and evaluation of chemotherapy-induced oral mucositis.

Experimental Design: Cheek pouches of 10 Syrian golden hamsters were imaged using OCT/ODT during development of chemotherapy-induced mucositis. I.p. injections of 5-fluorouracil and mechanical irritation induced oral lesions. At 2, 4, 7, and 11 days, one hamster was sacrificed and processed for histopathology. OCT images were visually examined; ODT results were semiquantified. Imaging data were compared with histologic findings.

Results: During the development of mucositis, OCT/ODT identified the following events: (a) change in epithelial thickness (beginning on day 2), (b) loss of surface keratinized layer continuity (beginning on day 4), (c) loss of epithelial (day 4 onwards) and submucosal integrity (day 7 onwards), (d) changes in axial blood flow velocity (increased on days 2 and 4; decreased on day 7), and (e) changes in blood vessel size (diameter doubled on day 2; quadrupled on day 4; unchanged on day 7). The semiquantitative imaging-based scoring system identified the severity of mucositis as defined by histopathology. The combination of imaging criteria used allowed for the detection of early, intermediate, and late mucositic changes. Imaging data gave higher scores compared with clinical scores early on, suggesting that the imaging-based diagnostic scoring was more sensitive to early mucositic change than the clinical scoring system. Once mucositis was established, imaging and clinical scores converged.

Conclusion: OCT/ODT identified chemotherapy-induced oral changes before their clinical manifestation, and the proposed scoring system for oral mucositis was validated for the semiquantification of mucositic change.
Polymorphisms of MTHFD, Plasma Homocysteine Levels, and Risk of Gastric Cancer in a High-Risk Chinese Population
Authors: Wang Lina , Ke Qiao , Chen Wensen , Wang Jianming , Tan Yongfei , Zhou Yan , Hua Zhaolai , Ding Weiliang , Niu Juying , Shen Jing , Zhang Zuofeng , Wang Xinru , Xu Yaochu , Shen Hongbing
Published: April 2007

Purpose: Accumulative evidence suggests that folate has a protective effect on gastric cancer. The methylenetetrahydrofolate dehydrogenase (MTHFD) plays an important role in folate and homocysteine metabolisms, and polymorphisms of MTHFD may result in disturbance of the folate-mediated homocysteine pathway. The aim of this study is to test the hypothesis that genetic variants of MTHFD and plasma homocysteine levels are associated with risk of gastric cancer and modulated by genotypes of methylenetetrahydrofolate reductase (MTHFR).

Experimental Design: We genotyped G1958A and T401C in MTHFD and C677T in MTHFR and detected total plasma homocysteine (tHcy) levels in a case-control study of 589 gastric cancer cases and 635 cancer-free controls in a high-risk Chinese population.

Results: The variant genotypes of MTHFD 1958AA and 401CC were associated with a significantly increased risk of gastric cancer [adjusted odds ratio (OR), 2.05; 95% confidence interval (95% CI), 1.34-3.13 for 1958AA; adjusted OR, 1.43; 95% CI, 1.14-1.80 for 401CC] compared with 1958GG/GA and 401TT/TC genotypes, respectively. Both of the effects were more evident in the subjects carrying MTHFR 677CT/TT genotypes. The average tHcy level was significantly higher in gastric cancer cases than in controls (P < 0.01), and the upper quartile of tHcy (>13.6 μmol/L) was associated with an 82% significantly increased risk of gastric cancer, compared with the lowest quartile of tHcy (≤8.0 μmol/L; adjusted OR, 1.82; 95% CI, 1.20-2.75).

Conclusions: The strong associations between MTHFD variants and the plasma tHcy levels and gastric cancer risk suggest, for the first time, a possible gene-environment interaction between genetic variants of folate-metabolizing genes and high tHcy levels in gastric carcinogenesis.
The Human T-Box Mesodermal Transcription Factor Brachyury Is a Candidate Target for T-Cell–Mediated Cancer Immunotherapy
Authors: Palena Claudia , Polev Dmitry E. , Tsang Kwong Y. , Fernando Romaine I. , Litzinger Mary , Krukovskaya Larisa L. , Baranova Ancha V. , Kozlov Andrei P. , Schlom Jeffrey
Published: April 2007

Purpose: Identification of tumor antigens is essential in advancing immune-based therapeutic interventions in cancer. Particularly attractive targets are those molecules that are selectively expressed by malignant cells and that are also essential for tumor progression.

Experimental Design and Results: We have used a computer-based differential display analysis tool for mining of expressed sequence tag clusters in the human Unigene database and identified Brachyury as a novel tumor antigen. Brachyury, a member of the T-box transcription factor family, is a key player in mesoderm specification during embryonic development. Moreover, transcription factors that control mesoderm have been implicated in the epithelial-mesenchymal transition (EMT), which has been postulated to be a key step during tumor progression to metastasis. Reverse transcription-PCR analysis validated the in silico predictions and showed Brachyury expression in tumors of the small intestine, stomach, kidney, bladder, uterus, ovary, and testis, as well as in cell lines derived from lung, colon, and prostate carcinomas, but not in the vast majority of the normal tissues tested. An HLA-A0201 epitope of human Brachyury was identified that was able to expand T lymphocytes from blood of cancer patients and normal donors with the ability to lyse Brachyury-expressing tumor cells.

Conclusions: To our knowledge, this is the first demonstration that (a) a T-box transcription factor and (b) a molecule implicated in mesodermal development, i.e., EMT, can be a potential target for human T-cell–mediated cancer immunotherapy.
Characterization and Magnetic Resonance Imaging of a Rat Model of Human B-Cell Central Nervous System Lymphoma
Authors: Soussain Carole , Muldoon Leslie L. , Varallyay Csanad , Jahnke Kristoph , DePaula Luciana , Neuwelt Edward A.
Published: April 2007

Purpose: The incidence of primary central nervous system lymphoma (PCNSL) is increasing. Therapeutic approaches remain controversial. An animal model that mimics the clinical situation would be useful for evaluating PCNSL biology and treatment.

Experimental Design: Nude rats received intracerebral (caudate nucleus, n = 49) or intraventricular (n = 4) inoculation of human B-lymphoma cell line MC116. Two to five weeks after tumor inoculation, magnetic resonance imaging (MRI) was done (n = 24), and rat brains were assessed for pathology. Five rats each received whole-brain radiotherapy (WBRT, 20 Gy) or high-dose i.v. methotrexate (3 g/m2).

Results: Intracerebral tumors developed in 84% of evaluable animals with no pretreatment, 79% of rats pretreated with 4 Gy total body irradiation, and 92% of rats pretreated with cyclophosphamide (300 mg/m2). MRI showed abnormal T2 signal and gadolinium enhancement on T1-weighted images, consistent with tumor growth 19 to 24 days after inoculation. Tumor cells staining positively for B-lymphoma markers infiltrated within the inoculated hemisphere, along fiber tracks to the contralateral hemisphere, and along the subarachnoid space and ventricles. Tumors showed reactive gliosis. Intraventricular tumor cell injection resulted in periventricular parenchymal infiltration in both hemispheres. Radiation and methotrexate were effective in vitro, but only WBRT was clearly effective after 1 week in the intracerebral model.

Conclusion: This model closely mimics human PCNSL in terms of imaging, histology, and treatment sensitivity and will be useful for the development of future therapeutic strategies for PCNSL.
Role of Heparin on TNF-α and IL-6 Levels in Liver Regeneration after Partial Hepatic Resection
Authors: Yuceturk H. , Yagmurdur M.C. , Gur G. , Demirbilek M. , Bilezikci B. , Turan M. , Karakayali H. , Haberal M.
Published: April 2007

Objectives: The aim of this study was to investigate the effect of heparin on TNF-α and interleukin (IL)-6 levels and the complement system in liver regeneration in a murine model. Materials and Methods: 32 Wistar albino female rats weighing between 180 and 250 g were included in the study. The rats were divided into four groups as follows: group 1, treated with partial (50%) hepatectomy and intravenous heparin 1,000 IU/kg in repeated daily doses; group 2, treated with sham operation and intravenous heparin 1,000 IU/kg in repeated daily doses; group 3, treated with partial (50%) hepatectomy, and group 4 (controls), treated with only sham operation. Before the surgical intervention and after a general anesthetic had been administered to all rats, blood was taken from the left ventricle of each rat, and each sample was assessed to determine total complement hemolytic activity (CH50/ml). On the 5th postoperative day, blood was taken to assess CH50 activity and the levels of TNF-α and IL-6 via ELISA. Each rat was then killed by decapitation after which gravimetric analysis and immunohistochemical staining for proliferating cell nuclear antigen (PCNA) were performed. Results: Serum CH50 activity of group 1 was 4% as compared to 51% in group 3 (p = 0.01). The serum TNF-α level of group 1 was 43 pg/ml as compared to 86 pg/ml in group 3 (p = 0.002). The serum IL-6 level of group 1 was 19 pg/ml as compared to 44 pg/ml in group 3 (p = 0.02). The serum IL-6 level of group 2 was 4 pg/ml as compared to 44 pg/ml in group 3 (p = 0.005). According to the results of gravimetric analysis, the mean regeneration rate of group 1 was 4.4% as compared to 22% of group 3 (p = 0.001). The mean PCNA index values of group 2 was the highest of all groups (p = 0.01). However, the mean PCNA index value of group 1 was the lowest of all groups (p = 0.01). Conclusion: Because of its anti-inflammatory action via the complement system, heparin produced an unfavorable effect on liver regeneration.
Evolution of Low-Level Angular Momentum in the 2 June 1995 Dimmitt, Texas, Tornado Cyclone
Authors: Rasmussen Erik N. , Straka Jerry M.
Published: April 2007

The life cycle of the 2 June 1995 Dimmitt, Texas, tornado cyclone, observed during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), is described. The tornado cyclone here is defined as a significantly axisymmetric flow larger than the visible tornado and characterized by increasing angular momentum with increasing radius. Its life cycle included three phases with somewhat differing evolution of angular momentum, herein called intensifying, transition, and weakening. During the intensifying stage, the funnel and debris cloud gradually increased in size. The azimuthally averaged secondary circulation of the larger-scale tornado cyclone, as determined using high-resolution single-Doppler data obtained by a mobile radar, was primarily inward and upward, consistent with the presence of a wall cloud outside the tornado. The azimuthally averaged angular momentum increased monotonically away from the tornado, so inward advection allowed the angular momentum to increase slowly with time in part of the tornado cyclone. During the transition phase, downdrafts began to occur within the tornado cyclone. The transport of angular momentum by the secondary circulation nearly was offset by eddy flux convergence of angular momentum so that the azimuthally averaged angular momentum tendency was only weakly negative at most radii. The tornado was visually impressive during this stage, featuring a 400-m diameter debris cloud extending to cloud base, while the surrounding wall cloud shrank and eroded. During the weakening phase, the funnel and debris cloud gradually shrank, and the funnel went through a rope stage prior to disappearing. The weakening phase was characterized by extensive downdrafts at all radii outside the tornado, and large-scale near-ground outflow as observed by mobile mesonet systems in a portion of the tornado cyclone. The secondary circulation acted to transport smaller angular momentum downward from aloft, and outward along the ground. All terms of the angular momentum budget became negative throughout most of the low-level (0–800-m AGL) tornado cyclone during the weakening phase. Several hypotheses for this evolution are evaluated, including changes in water loading in the tornado cyclone, cooling of the near-ground air, and the distribution of tangential velocity with height with its concomitant influence on the nonhydrostatic vertical pressure gradient force.
Optimal Perturbations in Quasigeostrophic Turbulence
Authors: DelSole Timothy
Published: April 2007

This paper tests the hypothesis that optimal perturbations in quasigeostrophic turbulence are excited sufficiently strongly and frequently to account for the energy-containing eddies. Optimal perturbations are defined here as singular vectors of the propagator, for the energy norm, corresponding to the equations of motion linearized about the time-mean flow. The initial conditions are drawn from a numerical solution of the nonlinear equations associated with the linear propagator. Experiments confirm that energy is concentrated in the leading evolved singular vectors, and that the average energy in the initial singular vectors is within an order of magnitude of that required to explain the average energy in the evolved singular vectors. Furthermore, only a small number of evolved singular vectors (4 out of 4000) are needed to explain the dominant eddy structure when total energy exceeds a predefined threshold. The initial singular vectors explain only 10% of such events, but this discrepancy was similar to that of the full propagator, suggesting that it arises primarily due to errors in the propagator. In the limit of short lead times, energy conservation can be expressed in terms of suitable singular vectors to constrain the energy distribution of the singular vectors in statistically steady equilibrium. This and other connections between linear optimals and nonlinear dynamics suggests that the positive results found here should carry over to other systems, provided the propagator and initial states are chosen consistently with respect to the nonlinear system.
Turbulent Fluxes in the Hurricane Boundary Layer. Part II: Latent Heat Flux
Authors: Drennan William M. , Zhang Jun A. , French Jeffrey R. , McCormick Cyril , Black Peter G.
Published: April 2007

As part of the recent ONR-sponsored Coupled Boundary Layer Air–Sea Transfer (CBLAST) Departmental Research Initiative, an aircraft was instrumented to carry out direct turbulent flux measurements in the high wind boundary layer of a hurricane. During the 2003 field season flux measurements were made during Hurricanes Fabian and Isabel. Here the first direct measurements of latent heat fluxes measured in the hurricane boundary layer are reported. The previous wind speed range for humidity fluxes and Dalton numbers has been extended by over 50%. Up to 30 m s−1, the highest 10-m winds measured, the Dalton number is not significantly different from the Humidity Exchange over the Sea (HEXOS) result, with no evidence of an increase with wind speed.
Refinements to Ice Particle Mass Dimensional and Terminal Velocity Relationships for Ice Clouds. Part I: Temperature Dependence
Authors: Heymsfield Andrew J. , Bansemer Aaron , Twohy Cynthia H.
Published: April 2007

This two-part study attempts to find appropriate mass dimension and terminal velocity relationships that, when considered together with particle size distributions (PSD), agree with coincident measurements of ice water content (IWC), and with variables related to higher moments such as the mean mass-weighted fall speed. Reliable relationships are required for improving microphysical parameterizations for weather forecast models and developing methods for evaluating them, subjects addressed in detail in Part II of this study.

Here, a range of values from 1.5 to 2.3 is assumed for the exponent b in the mass dimension relationship, m = aDb, where D is the maximum particle dimension, to bound its likely value for sizes above about 100 μm. Measured IWC and size spectra are used to find appropriate values for the coefficient a. It is demonstrated that all values of the exponent b, with appropriate a coefficients, can fit the IWC measurements. Coincident information on particle cross-sectional areas with the m(D) relationships is used to develop general fall velocity relationships of the form Vt = ADB. These assessments use five midlatitude, synoptically generated ice layers, and 10 low-latitude, convectively generated ice cloud layers, spanning the temperature range from −60° to 0°C.

The coefficients a and A and exponent B are represented in terms of the exponent b and are shown to be temperature-dependent for the synoptic clouds and relatively independent of it in the convective clouds, a result of particle mixing through the cloud column. Consistency is found with earlier results and with analytic considerations. It is found that the fall velocity is inversely proportional to the air density to approximately the exponent 0.54, close to values assumed in earlier studies.
Genesis of the Northeast Brazil Upper-Tropospheric Cyclonic Vortex: A Primitive Equation Barotropic Instability Study
Authors: Mishra S. K. , Rao V. Brahmananda , Franchito Sergio H.
Published: April 2007

The primitive equation barotropic unstable linear normal modes are computed using an eigenvalue approach for daily latitudinal profiles of zonal flow in the upper-tropospheric layer of 100–350 hPa before and after formation of cyclonic vortices during January 1993 and November 2001 off the coast of northeast Brazil. The wave kinetic energy equation for u- and υ-motion is presented. Equations are derived to isolate the contribution of divergence and other dynamical processes in the movement and growth of unstable modes. Numerical accuracy and physical nature of unstable modes are tested.

In a short span of 2–3 days, prior to formation of vortices, a progressive and a sharp intensification of the basic flow shear zone and its barotropic instability are seen with time. The horizontal structure, momentum transport, and zonal and meridional scales of the most unstable normalized wave are obtained and compared with the vortex extracted from the 200-hPa observed winds using a bandpass smoother. A close agreement is found between them. It is shown that the zonal and meridional scales of the preferred wave are related to the length scale of the shear zone. The wave is confined to the shear zone and its maximum amplitude is located at the latitude of maximum β − uyy. The role of divergence in the movement and growth of the wave is investigated. The energetics of the unstable wave u- and υ-motion is computed, and it is inferred that the energy source for the growth of wave u- (υ-) motion is the energy conversion (work done by pressure force), which lies in the shear zone.

It is emphasized that a deeper insight regarding the genesis of the cyclonic vortex can be gained on the basis of stability analysis of daily observed zonal flow profiles, which may not be possible using idealized or mean profiles. An explanation for nonmanifestation of the instability in the monthly mean flow is provided.
Refinements to Ice Particle Mass Dimensional and Terminal Velocity Relationships for Ice Clouds. Part II: Evaluation and Parameterizations of Ensemble Ice Particle Sedimentation Velocities
Authors: Heymsfield Andrew J. , van Zadelhoff Gerd-Jan , Donovan David P. , Fabry Frederic , Hogan Robin J. , Illingworth Anthony J.
Published: April 2007

This two-part study addresses the development of reliable estimates of the mass and fall speed of single ice particles and ensembles. Part I of the study reports temperature-dependent coefficients for the mass-dimensional relationship, m = aDb, where D is particle maximum dimension. The fall velocity relationship, Vt = ADB, is developed from observations in synoptic and low-latitude, convectively generated, ice cloud layers, sampled over a wide range of temperatures using an assumed range for the exponent b. Values for a, A, and B were found that were consistent with the measured particle size distributions (PSD) and the ice water content (IWC).

To refine the estimates of coefficients a and b to fit both lower and higher moments of the PSD and the associated values for A and B, Part II uses the PSD from Part I plus coincident, vertically pointing Doppler radar returns. The observations and derived coefficients are used to evaluate earlier, single-moment, bulk ice microphysical parameterization schemes as well as to develop improved, statistically based, microphysical relationships. They may be used in cloud and climate models, and to retrieve cloud properties from ground-based Doppler radar and spaceborne, conventional radar returns.
Relating Static Energy to Potential Temperature: A Caution
Authors: DeCaria Alex J.
Published: April 2007

The relationship between dry static energy and potential temperature, cpθ = cpT + gz, is exact for an adiabatic temperature profile, and extremely close to exact for an isothermal profile. Even though it is extremely accurate, its use in atmospheres with nonadiabatic temperature profiles can lead to significant errors when comparing the entropies of isolated atmospheric layers. Use of the relation in this context leads to the incorrect conclusion that an adiabatic temperature profile has greater entropy than an isothermal profile for the same static energy. The relation fails in this application because of the extreme sensitivity of the column-integrated entropy to temperature.
Twentieth-Century Trends in Runoff, Evapotranspiration, and Soil Moisture in the Western United States*
Authors: Hamlet Alan F. , Mote Philip W. , Clark Martyn P. , Lettenmaier Dennis P.
Published: April 2007

A physically based hydrology model is used to produce time series for the period 1916–2003 of evapotranspiration (ET), runoff, and soil moisture (SM) over the western United States from which long-term trends are evaluated. The results show that trends in ET in spring and summer are determined primarily by trends in precipitation and snowmelt that determine water availability. From April to June, ET trends are mostly positive due primarily to earlier snowmelt and earlier emergence of snow-free ground, and secondarily to increasing trends in spring precipitation. From July to September trends in ET are more strongly influenced by precipitation trends, with the exception of areas (most notably California) that receive little summer precipitation and have experienced large changes in snowmelt timing. Trends in the seasonal timing of ET are modest, but during the period 1947–2003 when temperature trends are large, they reflect a shift of ET from midsummer to early summer and late spring. As in other studies, it is found that runoff is occurring earlier in spring, a trend that is related primarily to increasing temperature, and is most apparent during 1947–2003. Trends in the annual runoff ratio, a variable critical to western water management, are determined primarily by trends in cool season precipitation, rather than changes in the timing of runoff or ET. It was found that the signature of temperature-related trends in runoff and SM is strongly keyed to mean midwinter [December–February (DJF)] temperatures. Areas with warmer winter temperatures show increasing trends in the runoff fraction as early as February, and colder areas as late as June. Trends toward earlier spring SM recharge are apparent and increasing trends in SM on 1 April are evident over much of the region. The 1 July SM trends are less affected by snowmelt changes and are controlled more by precipitation trends.
Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming
Authors: Yoshioka Masaru , Mahowald Natalie M. , Conley Andrew J. , Collins William D. , Fillmore David W. , Zender Charles S. , Coleman Dani B.
Published: April 2007

The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.
Analysis of the Dominant Mode of Convectively Coupled Kelvin Waves in the West African Monsoon
Authors: Mounier Flore , Kiladis George N. , Janicot Serge
Published: April 2007

The dominant mode of convectively coupled Kelvin waves has been detected over the Atlantic and Africa during northern summer by performing composite analyses on observational fields based on an EOF reconstructed convection index over West Africa. Propagating eastward, many waves originate from the Pacific sector, interact with deep convection of the marine ITCZ over the Atlantic and the continental ITCZ over West and central Africa, and then weaken over East Africa and the Indian Ocean. It has been shown that they are able to modulate the life cycle and track of individual westward-propagating convective systems. Their mean kinematic characteristics comprise a wavelength of 8000 km, and a phase speed of 15 m s−1, leading to a period centered on 6 to 7 days. The African Kelvin wave activity displays large seasonal variability, being highest outside of northern summer when the ITCZ is close to the equator, facilitating the interactions between convection and these equatorially trapped waves. The convective and dynamical patterns identified over the Atlantic and Africa show some resemblance to the theoretical equatorially trapped Kelvin wave solution on an equatorial β plane. Most of the flow is in the zonal direction as predicted by theory, and there is a tendency for the dynamical fields to be symmetric about the equator, even though the ITCZ is concentrated well north of the equator at the full development of the African monsoon. In the upper troposphere and the stratosphere, the temperature contours slope sharply eastward with height, as expected from an eastward-moving heat source that forces a dry Kelvin wave response. It is finally shown that the mean impact of African Kelvin waves on rainfall and convection is of the same level as African easterly waves.
Low-Level Cloud Variability over the Equatorial Cold Tongue in Observations and Models
Authors: Mansbach David K. , Norris Joel R.
Published: April 2007

Examination of cloud and meteorological observations from satellite, surface, and reanalysis datasets indicates that monthly anomalies in low-level cloud amount and near-surface temperature advection are strongly negatively correlated on the southern side of the equatorial Pacific cold tongue. This inverse correlation occurs independently of relationships between cloud amount and sea surface temperature (SST) or lower tropospheric static stability (LTS), and the combination of advection plus SST or LTS explains significantly more interannual cloud variability in a multilinear regression than does SST or LTS alone. Warm anomalous advection occurs when the equatorial cold tongue is well defined and the southeastern Pacific trade winds bring relatively warm air over colder water. Ship meteorological reports and soundings show that the atmospheric surface layer becomes stratified under these conditions, thus inhibiting the upward mixing of moisture needed to sustain cloudiness against subsidence and entrainment drying. Cold anomalous advection primarily occurs when the equatorial cold tongue is weak or absent and the air–sea temperature difference is substantially negative. These conditions favor a more convective atmospheric boundary layer, greater cloud amount, and less frequent occurrence of clear sky.

Examination of output from global climate models developed by the Geophysical Fluid Dynamics Laboratory (GFDL) and the National Center for Atmospheric Research (NCAR) indicates that both models generally fail to simulate the cloud–advection relationships observed on the northern and southern sides of the equatorial cold tongue. Although the GFDL atmosphere model does reproduce the expected signs of cloud-advection correlations when forced with prescribed historical SST variations, it does not consistently do so when coupled to an ocean model. The NCAR model has difficulty reproducing the observed correlations in both atmosphere-only and coupled versions. This suggests that boundary layer cloud parameterizations could be improved through better representation of the effects of advection over varying SST.