bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Mexiletine on Electrical Field Stimulation-Induced Contractile Responses in the Ipsilateral and Contralateral Vasa Deferentia after Unilateral Testicular Torsion/Detorsion
Authors: Özen İbrahim Onur , Vural İsmail Mert , Moralıoğlu Serdar , Barun Süreyya , Ercan Zeynep Sevim , Sarıoğlu Yusuf
Published: August 2006

Aim: To investigate testicular torsion-induced changes on the electrical field stimulation (EFS)-induced contractions in rabbit vasa deferentia and to evaluate the effect of mexiletine. Methods: 18 male New Zealand albino rabbits were used in this experiment. Rabbits were divided into three groups: (1) control group (n = 6); (2) torsion group (n = 6), and (3) mexiletine group (n = 6). In the control group, vasa deferentia on both sides were harvested. In the torsion and mexiletine groups, the left testes of the rabbits were subjected to 720° of clockwise torsion for 2 h and then detorsion was performed. In the mexiletine group, 50 mg/kg i.p. mexiletine was administered 1 h before detorsion. Following 24 h of the torsion, vasa deferentia on both sides were harvested and 2-cm strips including both the prostatic and epididymal portions were prepared to record EFS-induced contractions. Results: Testicular torsion caused a significant inhibition in both phases of EFS-induced biphasic contractions of the ipsi- and contralateral vasa deferentia. Mexiletine treatment did not affect these inhibitory responses. Torsion/detorsion of the spermatic cord did not alter exogenously applied noradrenaline-induced contractions in both vasa deferentia. However, KCl-induced contractions diminished significantly in ipsilateral vas deferens of the torsion group and mexiletine restored this inhibition. Conclusions: Unilateral testicular torsion/detorsion leads to inhibition in both phases of EFS-induced biphasic contractions of the ipsi- and contralateral vasa deferentia by causing a defect in presynaptic nerve transmission. However, mexiletine has no effect on this inhibition. Inhibition of the KCl-induced contractions in the ipsilateral vas deferens, which indicates postsynaptic tissue damage, is restored by administering mexiletine 1 h prior to detorsion.
Relation of Age-Related Macular Degeneration and Cognitive Impairment in an Older Population
Authors: Pham Thuan Quoc , Kifley Annette , Mitchell Paul , Wang Jie Jin
Published: August 2006

Background: The aetiology of age-related macular degeneration (AMD) and cognitive impairment is poorly understood. A link between cognitive impairment and AMD has been proposed although only a weak association was found in population-based studies. Purpose: To assess cross-sectional associations between AMD and cognitive impairment in an older Australian population. Methods: The Blue Mountains Eye Study examined 3,509 persons aged 49+ years during 1997–2000. AMD lesions were assessed from retinal photographs using the Wisconsin System. Mini-mental state examination (MMSE), demographics, lifestyle factors and medical history were collected at interview. MMSE score was categorised as high-normal (28–30), low-normal (24–27) and impaired (<24). A modified MMSE excluded five vision related items and was dichotomised as normal (18–22) and impaired (0–17). Logistic regression was used to assess associations after adjusting for age, sex, visual impairment, stroke, current smoking status, hypertension, alcohol consumption and post-high-school qualification. Results: Prevalence rates for late and early AMD were 1.5% (n = 50) and 8.3% (n = 273), respectively. Cognitive impairment was present in 18.0% in persons with late AMD and 8.4% with early AMD, compared to 2.6% in persons without AMD. After multivariate adjustment, late AMD was associated with low normal MMSE (odds ratio (OR): 2.2, 95% confidence interval (CI): 1.1–5.0) and cognitive impairment (OR: 3.7, CI: 1.3–10.6). Using the modified MMSE, the multivariate association between late AMD and cognitive impairment remained (OR: 2.2, CI: 1.0–5.0). No significant association was found between cognitive impairment and early AMD. Conclusions: We found a significant, cross-sectional association between late AMD and cognitive impairment in a sample of older Australians that appeared to be independent of visual impairment. The association was weaker but remained significant after excluding vision-related items from the MMSE.
Determinants of Carotid Plaque Occurrence
Authors: Prati Patrizio , Vanuzzo Diego , Casaroli Marco , Bader Giovanni , Mos Lucio , Pilotto Lorenza , Canciani Luigi , Ruscio Maurizio , Touboul Pierre-Jean
Published: August 2006

Background: Increased carotid intima media thickness (CIMT) is frequently associated with established modifiable and non-modifiable cardiovascular risk factors, and is thought to be an independent predictor of ischemic cerebrovascular and cardiac events. The presence of carotid plaque is considered an established feature of atherosclerosis. There exist few longitudinal data on the predictive role of CIMT in the occurrence of carotid plaque. Methods: We restudied the survivors of a cohort of the San Daniele Project, a large randomized general population study, investigated in 1990 regarding the prevalence and determinants of carotid atherosclerosis. Using ultrasonography, we determined in 1,193 subjects (548 men and 645 women), the common carotid IMT and the presence of non-stenotic and stenotic plaque. Results: In 795 subjects without plaques or previous ischemic events at baseline, we found in multivariate analysis that CIMT ≧1 mm, age, hypertension and history of smoking are significant predictive elements of the occurrence of a new carotid plaque. The incremental probability of plaque occurrence is greater in midlife. CIMT and age are the most predictive risk factors with ORs of 3.66 (95% CI 1.4–9.4) and 3.02 (95% CI 2.4–3.7), respectively. The ORs for hypertension and smoking account for 1.5 (95% CI 1.1–3.4) and 1.7 (95% CI 1.1–2.8), respectively. Conclusions: Age, hypertension, history of smoking and B-mode detection of CIMT increases in subjects without carotid atherosclerosis and free of previous vascular events predict the occurrence of carotid atherosclerotic plaque.
Eligibility for Recombinant Tissue Plasminogen Activator in Acute Ischemic Stroke
Authors: Huang Poyin , Chen Chun-Hung , Yang Yuan-Han , Lin Ruey-Tay , Lin Feng-Cheng , Liu Ching-Kuan
Published: August 2006

Background: The eligibility for recombinant tissue plasminogen activator (rtPA) is rare. We analyze the reasons for exclusion from rtPA among patients who were admitted to our hospital within 3 h. Methods: A strict protocol for hyperacute stroke was set in a university teaching hospital. Consecutive patients activating the protocol from June 2004 to October 2005 were prospectively registered and entered into a computerized database. The patients were excluded from rtPA according to the modified exclusion criteria from the National Institute of Neurological Disorders and Stroke rtPA trial. Results: Of the 182 patients activating the protocol, only 11 (6.04%) received intravenous rtPA and 4 (2.2%) IA thrombolysis. Patients were excluded for multiple reasons, and the main reasons for exclusion were minor or improving stroke (46.15%), hypertension (35.16%), insufficient time to complete studies or onset beyond 3 h after reconfirmation (24.17%) and intracranial hemorrhage (15.93%). Of 167 excluded patients, 72 (43.11%) were excluded by a single criterion, 53 (31.73%) by 2 criteria and 29 (17.36%) by 3 criteria. The mean time from hospital arrival to presentation to a neurologist was 9.24 ± 15.11 min (n = 164, median = 8.00, mode = 10, range = 0–65). The mean time from hospital arrival to computed tomography (CT) was 21.67 ± 23.95 min (n = 167, median = 20.00, mode = 10, range = 4–68). Conclusion: An intrahospital stroke code was implemented to minimize intrahospital delay. However, only 11 patients received intravenous rtPA and 4 IA thrombolysis at our hospital from June 2004 to October 2005. The result brings into question the neurologist’s conservative interpretation of the criteria and the necessity to clearly define some criteria. Furthermore an intrahospital stroke code should also be implemented for inpatients to maximize the eligibility for rtPA.
Intravenous Thrombolysis in German Stroke Units before and after Regulatory Approval of Recombinant Tissue Plasminogen Activator
Authors: Weimar C. , Kraywinkel K. , Maschke M. , Diener H.-C.
Published: August 2006

Background: Intravenous thrombolysis with recombinant tissue plasminogen activator (rt-PA) within 3 h after onset of focal cerebral ischemia was approved in Germany in August 2000. Methods: 11 neurology departments with acute stroke units participated in the German Stroke Study Collaboration before (n = 2,925) and after (n = 3,204) approval of rt-PA in Germany and consecutively registered all patients admitted within 24 h following acute ischemic stroke. Results: Frequency of intravenous thrombolysis in patients admitted within 24 h after symptom onset increased from 4.8% before approval to 7.9% after approval of rt-PA. Among patients treated with rtPA, age increased significantly and the delay between symptom onset and imaging was significantly shorter in the second study period. Conclusions: The observed improvement in management and quantity of intravenous thrombolysis may be explained by greater experience and greater legal security following regulatory approval of rtPA.
Clustering of Risk Factors Increases the Incidence of Echolucent Carotid Plaque in Stroke Patients
Authors: Yamashiro Kazuo , Watanabe Terubumi , Tanaka Ryota , Komine-Kobayashi Miki , Mizuno Yoshikuni , Urabe Takao
Published: August 2006

Background: The purpose of this study was to assess the influence of clusters of risk factors on the incidence of echolucent carotid plaque in stroke patients. Methods: A retrospective analysis of 413 stroke patients who had undergone carotid ultrasonography was performed. High-resolution B-mode ultrasonography was used to evaluate the characteristics of carotid plaque. We investigated the relationships between the incidence of echolucent carotid plaque and clustering of risk factors (hypertension, diabetes mellitus and hyperlipidemia) and stroke subtypes and transient ischemic attack (TIA). Results: Echolucent plaques were present in 10.5% of patients free of risk factors, in 18.8% with a single risk factor (NS), in 27.7% with two risk factors (p <0.01) and in 50.0% with three risk factors (p <0.001), and were significantly more common in patients with multiple risk factors (odds ratio 1.79; 95% CI, 1.05–3.06; p = 0.045). Echolucent plaques were observed in 41.2% of patients with atherothrombotic infarction, in 17.6% with lacunar infarction, in 11.5% with cardioembolic stroke, and in 25.0% with TIA, and were significantly more common in patients with atherothrombotic infarction than in those with lacunar infarction or cardioembolic stroke (p<0.001), or in those with TIA (p <0.05). Conclusions: The clustering of risk factors increased the incidence of echolucent carotid plaque. Patients with multiple risk factors were at increased risk of echolucent plaque, and these had a significant relationship with atherothrombotic infarction compared with other stroke subtypes and TIA.
Serial Measurements of N-Terminal pro-Brain Natriuretic Peptide after Acute Ischemic Stroke
Authors: Jensen J.K. , Mickley H. , Bak S. , Korsholm L. , Kristensen S.R.
Published: August 2006

Background: The exact time-course of N-terminal pro-brain natriuretic peptide (NT-proBNP) and the prognostic importance in the immediate phase of ischemic stroke have not been established. Methods: NT-proBNP was measured daily from admission to day 5 and again at 6-month follow-up in 250 consecutive patients with acute ischemic stroke. Results: NT-proBNP peaked the day after onset of symptoms (p = 0.007) followed by a decrease until day 5 (p = 0.001, ANOVA). At 6-month follow-up the difference in the level of NT-proBNP was unchanged compared to day 5 (p = 0.42). NT-proBNP levels ≧615 pg/ml at day 2 after onset of symptoms was associated with 6-month mortality. Conclusion: NT-proBNP peaks the day after onset of symptoms in patients with acute ischemic stroke. A single measurement of NT-proBNP appears to be an indicator of 6-month mortality.
Roles of Paraoxonase and Oxidative Stress in Adolescents with Uraemic, Essential or Obesity-Induced Hypertension
Authors: Baráth Ákos , Németh Ilona , Karg Eszter , Endreffy Emőke , Bereczki Csaba , Gellén Balázs , Haszon Ibolya , Túri Sándor
Published: August 2006

Background/Aims: Paraoxonase 1 (PON1) is associated with high-density lipoproteins in the plasma, and is capable of hydrolysing oxidized lipids and preventing the oxidation of low-density lipoproteins. Oxidative stress and the PON1 (activity and Q192R polymorphism) were analysed in adolescent patients with essential (n = 49) or obesity-induced hypertension (n = 79), uraemic patients (n = 20), and also in obese normotensive patients (n = 60) and age-matched controls (n = 57). Methods: The PON1 activity was measured via paraoxon hydrolysis. The PON1 genotype was determined by real-time PCR. The levels of oxidized and reduced glutathione, the end-products of nitric oxide, cysteine, homocysteine and lipid peroxidation in the plasma were measured and related to the PON1 status. Results: There were no significant differences between the patient groups and the control group in the genotype distributions and the allele frequencies of the Q192R polymorphism. The PON activity was significantly lower (p < 0.001) in the uraemic hypertensive group than in the controls. The MDA concentration was significantly higher in the uraemic hypertensive (p < 0.001) and obese hypertensive (p < 0.05) patients. The plasma NOx concentrations were significantly lower (p < 0.001) and the ratio MDA/NOx were significantly higher in all four patient groups. The GSH levels were significantly lower in the patients with hypertension (p < 0.001) and obesity-induced hypertension (p < 0.05) than in the controls, while the GSSG level (p < 0.01) and the ratio GSSG/GSH (p < 0.05) was significantly higher in the uraemic hypertensive group. The plasma homocysteine level was significantly higher (p < 0.001) in the uraemic hypertensive patients as compared with the controls. Conclusions: We found no significant correlation between the biochemical parameters and neither genotypes nor enzyme activities. The PON1 status and the levels of certain biochemical parameters are independently associated with the hypertension in hypertensive and obese hypertensive patients, and the elevated levels of lipid peroxides and plasma homocysteine may contribute to the increased risk of cardiovascular complications in patients on haemodialysis.
Consistency of Pseudolikelihood Estimation of Fully Visible Boltzmann Machines
Authors: Hyvärinen Aapo
Published: August 2006

A Boltzmann machine is a classic model of neural computation, and a number of methods have been proposed for its estimation. Most methods are plagued by either very slow convergence or asymptotic bias in the resulting estimates. Here we consider estimation in the basic case of fully visible Boltzmann machines. We show that the old principle of pseudolikelihood estimation provides an estimator that is computationally very simple yet statistically consistent.
Images, Frames, and Connectionist Hierarchies
Authors: Dayan Peter
Published: August 2006

The representation of hierarchically structured knowledge in systems using distributed patterns of activity is an abiding concern for the connectionist solution of cognitively rich problems. Here, we use statistical unsupervised learning to consider semantic aspects of structured knowledge representation. We meld unsupervised learning notions formulated for multilinear models with tensor product ideas for representing rich information. We apply the model to images of faces.
Properties of Synergies Arising from a Theory of Optimal Motor Behavior
Authors: Chhabra Manu , Jacobs Robert A.
Published: August 2006

We consider the properties of motor components, also known as synergies, arising from a computational theory (in the sense of Marr, 1982) of optimal motor behavior. An actor's goals were formalized as cost functions, and the optimal control signals minimizing the cost functions were calculated. Optimal synergies were derived from these optimal control signals using a variant of nonnegative matrix factorization. This was done using two different simulated two-joint arms—an arm controlled directly by torques applied at the joints and an arm in which forces were applied by muscles—and two types of motor tasks—reaching tasks and via-point tasks.

Studies of the motor synergies reveal several interesting findings. First, optimal motor actions can be generated by summing a small number of scaled and time-shifted motor synergies, indicating that optimal movements can be planned in a low-dimensional space by using optimal motor synergies as motor primitives or building blocks. Second, some optimal synergies are task independent—they arise regardless of the task context—whereas other synergies are task dependent—they arise in the context of one task but not in the contexts of other tasks. Biological organisms use a combination of task-independent and task-dependent synergies. Our work suggests that this may be an efficient combination for generating optimal motor actions from motor primitives. Third, optimal motor actions can be rapidly acquired by learning new linear combinations of optimal motor synergies. This result provides further evidence that optimal motor synergies are useful motor primitives. Fourth, synergies with similar properties arise regardless if one uses an arm controlled by torques applied at the joints or an arm controlled by muscles, suggesting that synergies, when considered in “movement space,” are more a reflection of task goals and constraints than of fine details of the underlying hardware.
Recognition by Variance: Learning Rules for Spatiotemporal Patterns
Authors: Barak Omri , Tsodyks Misha
Published: August 2006

Recognizing specific spatiotemporal patterns of activity, which take place at timescales much larger than the synaptic transmission and membrane time constants, is a demand from the nervous system exemplified, for instance, by auditory processing. We consider the total synaptic input that a single readout neuron receives on presentation of spatiotemporal spiking input patterns. Relying on the monotonic relation between the mean and the variance of a neuron's input current and its spiking output, we derive learning rules that increase the variance of the input current evoked by learned patterns relative to that obtained from random background patterns. We demonstrate that the model can successfully recognize a large number of patterns and exhibits a slow deterioration in performance with increasing number of learned patterns. In addition, robustness to time warping of the input patterns is revealed to be an emergent property of the model. Using a leaky integrate-and-fire realization of the readout neuron, we demonstrate that the above results also apply when considering spiking output.
Estimating Spiking Irregularities Under Changing Environments
Authors: Miura Keiji , Okada Masato , Amari Shun-ichi
Published: August 2006

We considered a gammadistribution of interspike intervals as a statistical model for neuronal spike generation. A gamma distribution is a natural extension of the Poisson process taking the effect of a refractory period into account. The model is specified by two parameters: a time-dependent firing rate and a shape parameter that characterizes spiking irregularities of individual neurons. Because the environment changes over time, observed data are generated from a model with a time-dependent firing rate, which is an unknown function. A statistical model with an unknown function is called a semiparametric model and is generally very difficult to solve. We used a novel method of estimating functions in information geometry to estimate the shape parameter without estimating the unknown function. We obtained an optimal estimating function analytically for the shape parameter independent of the functional form of the firing rate. This estimation is efficient without Fisher information loss and better than maximum likelihood estimation. We suggest a measure of spiking irregularity based on the estimating function, which may be useful for characterizing individual neurons in changing environments.
Spatiotemporal Structure in Large Neuronal Networks Detected from Cross-Correlation
Authors: Schneider Gaby , Havenith Martha N. , Nikolić Danko
Published: August 2006

The analysis of neuronal information involves the detection of spatiotemporal relations between neuronal discharges. We propose a method that is based on the positions (phase offsets) of the central peaks obtained from pairwise cross-correlation histograms. Data complexity is reduced to a one-dimensional representation by using redundancies in the measured phase offsets such that each unit is assigned a “preferred firing time” relative to the other units in the group. We propose two procedures to examine the applicability of this method to experimental data sets. In addition, we propose methods that help the investigation of dynamical changes in the preferred firing times of the units. All methods are applied to a sample data set obtained from cat visual cortex.
Stable Competitive Dynamics Emerge from Multispike Interactions in a Stochastic Model of Spike-Timing-Dependent Plasticity
Authors: Appleby Peter A. , Elliott Terry
Published: August 2006

In earlier work we presented a stochastic model of spike-timing-dependent plasticity (STDP) in which STDP emerges only at the level of temporal or spatial synaptic ensembles. We derived the two-spike interaction function from this model and showed that it exhibits an STDP-like form. Here, we extend this work by examining the general n-spike interaction functions that may be derived from the model. A comparison between the two-spike interaction function and the higher-order interaction functions reveals profound differences. In particular, we show that the two-spike interaction function cannot support stable, competitive synaptic plasticity, such as that seen during neuronal development, without including modifications designed specifically to stabilize its behavior. In contrast, we show that all the higher-order interaction functions exhibit a fixed-point structure consistent with the presence of competitive synaptic dynamics. This difference originates in the unification of our proposed “switch” mechanism for synaptic plasticity, coupling synaptic depression and synaptic potentiation processes together. While three or more spikes are required to probe this coupling, two spikes can never do so. We conclude that this coupling is critical to the presence of competitive dynamics and that multispike interactions are therefore vital to understanding synaptic competition.
A State-Space Analysis for Reconstruction of Goal-Directed Movements Using Neural Signals
Authors: Srinivasan Lakshminarayan , Eden Uri T. , Willsky Alan S. , Brown Emery N.
Published: August 2006

The execution of reaching movements involves the coordinated activity of multiple brain regions that relate variously to the desired target and a path of arm states to achieve that target. These arm states may represent positions, velocities, torques, or other quantities. Estimation has been previously applied to neural activity in reconstructing the target separately from the path. However, the target and path are not independent. Because arm movements are limited by finite muscle contractility, knowledge of the target constrains the path of states that leads to the target. In this letter, we derive and illustrate a state equation to capture this basic dependency between target and path. The solution is described for discrete-time linear systems and gaussian increments with known target arrival time. The resulting analysis enables the use of estimation to study how brain regions that relate variously to target and path together specify a trajectory. The corresponding reconstruction procedure may also be useful in brain-driven prosthetic devices to generate control signals for goal-directed movements.
What Is the Relation Between Slow Feature Analysis and Independent Component Analysis?
Authors: Blaschke Tobias , Berkes Pietro , Wiskott Laurenz
Published: August 2006

We present an analytical comparison between linear slow feature analysis and second-order independent component analysis, and show that in the case of one time delay, the two approaches are equivalent. We also consider the case of several time delays and discuss two possible extensions of slow feature analysis.
Nonlocal Estimation of Manifold Structure
Authors: Bengio Yoshua , Monperrus Martin , Larochelle Hugo
Published: August 2006

We claim and present arguments to the effect that a large class of manifold learning algorithms that are essentially local and can be framed as kernel learning algorithms will suffer from the curse of dimensionality, at the dimension of the true underlying manifold. This observation invites an exploration of nonlocal manifold learning algorithms that attempt to discover shared structure in the tangent planes at different positions. A training criterion for such an algorithm is proposed, and experiments estimating a tangent plane prediction function are presented, showing its advantages with respect to local manifold learning algorithms: it is able to generalize very far from training data (on learning handwritten character image rotations), where local nonparametric methods fail.
Dynamics and Topographic Organization of Recursive Self-Organizing Maps
Authors: Tiňo Peter , Farkaš Igor , van Mourik Jort
Published: August 2006

Recently there has been an outburst of interest in extending topographic maps of vectorial data to more general data structures, such as sequences or trees. However, there is no general consensus as to how best to process sequences using topographic maps, and this topic remains an active focus of neurocomputational research. The representational capabilities and internal representations of the models are not well understood. Here, we rigorously analyze a generalization of the self-organizing map (SOM) for processing sequential data, recursive SOM(RecSOM) (Voegtlin, 2002), as a nonautonomous dynamical system consisting of a set of fixed input maps. We argue that contractive fixed-input maps are likely to produce Markovian organizations of receptive fields on the RecSOM map. We derive bounds on parameter β (weighting the importance of importing past information when processing sequences) under which contractiveness of the fixed-input maps is guaranteed. Some generalizations of SOM contain a dynamic module responsible for processing temporal contexts as an integral part of the model. We show that Markovian topographic maps of sequential data can be produced using a simple fixed (nonadaptable) dynamic module externally feeding a standard topographic model designed to process static vectorial data of fixed dimensionality (e.g., SOM). However, by allowing trainable feedback connections, one can obtain Markovian maps with superior memory depth and topography preservation. We elaborate on the importance of non-Markovian organizations in topographic maps of sequential data.
On the Consistency of the Blocked Neural Network Estimator in Time Series Analysis
Authors: Sarishvili A. , Andersson Ch. , Franke J. , Kroisandt G.
Published: August 2006

We describe a nonlinear regression problem, where the regression functions have an additive structure and the dependent variable is a one-dimensional time series. Multivariate time series with unknown time delay operators are used as independent variables. By fitting a feedforward neural network with block structure to the data, we estimated the additive regression function and, parallel to this, the time lags. We present the consistency proof of neural network weights estimator and the time lag estimator independently from each other. In the practical part of the article, we present the useful feature of blocked neural networks to estimate the relevance measures of each input variable in a simple way. Furthermore, we propose an approach to solve the well-known variable selection problem for the class of nonlinear multivariate beta-mixing time series models considered here. Finally, we apply the methodology to an artificial example.
On the Use of Lidar Images of Smoke Plumes to Measure Dispersion Parameters in the Stable Boundary Layer
Authors: Hiscox April L. , Nappo Carmen J. , Miller David R.
Published: August 2006

In this note a methodology is presented for measuring dispersion parameters based on lidar images, which can be used as an efficient way to remotely monitor time variations of plume dispersion parameters. Lidar images of a smoke plume cross section over a forest canopy during nighttime conditions are analyzed to estimate vertical dispersion parameters and vertical meander of the plume centerline in the near field. Dispersion parameters 60 m downwind are found to have a median value of 2.31 m, with values ranging from a minimum of 0.56 m to a maximum of 5.45 m. Measurements of these parameters have not previously been made outside the restraints of a wind tunnel experiment.
Improved Level-3 Oceanic Rainfall Retrieval from Dual-Frequency Spaceborne Radar Altimeter Systems
Authors: Tournadre J.
Published: August 2006

Since the launch of the Ocean Topography Experiment (TOPEX)/Poseidon in 1992, several studies have demonstrated that dual-frequency altimeter measurements cannot only accurately detect rain events but can also be used to infer quantitative values. The main problems with these techniques are the limited time and space sampling of nadir-looking instruments and the uncertainty in the height of the freezing level necessary to infer the surface rain rate from the measured signal attenuation. In addition to radar altimeters, altimetric satellites carry microwave radiometers designed to correct for atmospheric water effects. Using a radiative transfer model and simplified rainy atmospheres, a method of inversion of the microwave brightness temperatures in terms of freezing level is presented. The surface rain rate is then computed from the altimeter attenuation and the radiometer freezing level. The rain climatology is computed for the three altimeters currently in operation using a mixed lognormal distribution. Comparison with the Global Precipitation Climatology Project and Special Sensor Microwave Imager (SSM/I) climatologies shows that the use of freezing level greatly improves the altimeter climatology, which is of the same quality as that of the SSM/I for annual mean. The merging of the three altimeters is investigated. The resulting monthly mean rain rates are comparable to those derived from SSM/I. The high along-track resolution of altimeters also allows the determination of the length of rain events. The mean length is close to the SSM/I footprint size in the Tropics, but at higher latitude 80% of the rain has length scales smaller than 10 km, which might explain the relative underestimation of the mean rain rate by SSM/I.
Sources of Errors in Rainfall Measurements by Polarimetric Radar: Variability of Drop Size Distributions, Observational Noise, and Variation of Relationships between R and Polarimetric Parameters
Authors: Lee Gyu Won
Published: August 2006

Using a set of long-term disdrometric data and of actual radar measurements from the McGill S-band operational polarimetric radar, several sources of errors in rain measurement with polarimetric radar are explored in order to investigate their relative importance and the feasibility of a polarimetric technique for estimating R in the context of the McGill S-band operational radar that performs a full volume scan of 24 plan position indicators (PPIs) every 5 min. The sources of errors considered are the variability of drop size distributions (DSDs), observational noise, and systematic variation of the relationships between R and polarimetric parameters at different climate regimes.

Additional polarimetric parameters dramatically reduce the effect of the DSD variability on rain estimates by radar. The effectiveness of various multiparameter relationships is investigated. The relationships from the literature that are derived from the DSD model and measured DSDs at a different climate regime differ from those derived from the disdrometric dataset herein. An application of these relationships to the Montreal dataset results in a bias (about 10%–20%) and the significant random error resulting from the DSD variability. These errors should be eliminated by using a relationship suitable for the local climate.

Assuming a measurement noise as expected from a slow scanning polarimetric radar [∼1 rotation per minute (rpm)] and a 10-min smoothing, the R − (Zh, ZDR) relationship outperforms the conventional R − Zh because of the combined effect of the DSD variability and measurement errors. In addition, the marginal measurement noise that is required to have the same accuracy of R − Zh and R − (Zh, ZDR) algorithms is obtained as a function of temporal smoothing. The quantified measurement noise of the McGill S-band fast scanning operational radar (∼6 rpm) is significantly larger than that of a slow scanning radar, implying that a temporal averaging of ZDR of 1 h is needed to achieve some gain with R − (Zh, ZDR).
A Chemical Ionization Mass Spectrometer for Ground-Based Measurements of Nitric Acid
Authors: Kita Kazuyuki , Morino Yu , Kondo Yutaka , Komazaki Yuichi , Takegawa Nobuyuki , Miyazaki Yuzo , Hirokawa Jun , Tanaka Shigeru , Thompson Thomas L. , Gao Ru-Shan , Fahey David W.
Published: August 2006

A chemical ionization mass spectrometer (CIMS) instrument has been developed for high-precision measurements of gaseous nitric acid (HNO3) specifically under high- and variable-humidity conditions in the boundary layer. The instrument’s background signals (i.e., signals detected when HNO3-free air is measured), which depend on the humidity and HNO3 concentration of the sample air, are the most important factor affecting the limit of detection (LOD). A new system to provide HNO3-free air without changing both the humidity and the pressure of the sampled air was developed to measure the background level accurately. The detection limit was about 23 parts per trillion by volume (pptv) for 50-s averages. Field tests, including an intercomparison with the diffusion scrubber technique, were carried out at a surface site in Tokyo, Japan, in October 2003 and June 2004. A comparison between the measured concentrations of HNO3 and particulate nitrate indicated that the interference from particulate nitrate was not detectable (i.e., less than about 1%). The intercomparison indicated that the two independent measurements of HNO3 agreed to within the combined uncertainties of these measurements. This result demonstrates that the CIMS instrument developed in this study is capable of measuring HNO3 mixing ratios with the precision, accuracy, and time resolution required for atmospheric science.
In Situ Cloud Sensing with Multiple Scattering Lidar: Design and Validation of an Airborne Sensor
Authors: Evans K. Franklin , O’Connor Darren , Zmarzly Pat , Lawson R. Paul
Published: August 2006

The in situ cloud lidar is designed to measure cloud volumes of millions of cubic meters to overcome the sampling limitations of traditional cloud probes in inhomogeneous clouds. This technique sends laser pulses horizontally from an aircraft inside an optically thick cloud and measures the time series of the multiply scattered light with wide field-of-view detectors viewing upward and downward. The extinction in liquid clouds averaged over tens to hundreds of meters and the distance to cloud boundaries can be retrieved from the signal measured by a single-wavelength in situ lidar. This paper describes the design and operation of an in situ cloud lidar. A laser in the aircraft cabin outputs 532-nm wavelength pulses at 10 Hz, which are sent through beam-expanding optics for eye safety. The upward- and downward-viewing detectors use photomultiplier tubes and operate with either daytime (3° half angle; 0.37-nm solar-blocking filter) or nighttime (30°) optics. Example daytime lidar signals in dense cloud have a dynamic range of 1000 after solar background subtraction. Results from a nighttime flight in marine stratus are analyzed in detail. The variations in the lidar signals with aircraft travel are much smoother for the longer photon travel times, indicating that the later times sample volumes hundreds of meters in size. Extinction retrievals for 25-m-radius volumes have high correlation (R2 = 0.84) with Forward Scattering Spectrometer Probe (FSSP)-derived extinction, while the correlation is relatively low (R2 = 0.40) for 200-m volumes due to cloud inhomogeneity. Lidar retrievals of cloud-base and -top height from inside the cloud are consistent with cloud boundaries obtained from aircraft penetrations on ascents and descents.
Performance Assessment of the World Wide Lightning Location Network (WWLLN), Using the Los Alamos Sferic Array (LASA) as Ground Truth
Authors: Jacobson Abram R. , Holzworth Robert , Harlin Jeremiah , Dowden Richard , Lay Erin
Published: August 2006

The World Wide Lighting Location Network (WWLLN) locates lightning globally, using sparsely distributed very low frequency (VLF) detection stations. Due to WWLLN’s detection at VLF (in this case ∼10 kHz), the lightning signals from strong strokes can propagate up to ∼104 km to WWLLN sensors and still be suitable for triggering a station. A systematic evaluation of the performance of WWLLN is undertaken, using a higher-frequency (0–500 kHz) detection array [the Los Alamos Sferic Array (LASA)] as a ground truth during an entire thunderstorm season in a geographically confined case study in Florida. It is found that (a) WWLLN stroke-detection efficiency rises sharply to several percent as the estimated lightning current amplitude surpasses ∼30 kA; (b) WWLLN spatial accuracy is around 15 km, good enough to resolve convective-storm cells within a larger storm complex; (c) WWLLN is able to detect intracloud and cloud-to-ground discharges with comparable efficiency, as long as the current is comparable; (d) WWLLN detects lightning-producing storms with high efficiency in every 3-h epoch; thus, WWLLN can be useful for locating deep convection for weather forecasting on 3-h update cycles; and (e) WWLLN detects a stroke count in each storm that is weakly proportional to the stroke count detected by LASA. Thus, to the extent that lightning rate can serve as a statistical proxy for rainfall, WWLLN may eventually provide rainfall-proxy data to be assimilated in 3-h forecast update cycles.
Simulated Doppler Velocity Signatures of Evolving Tornado-Like Vortices
Authors: Davies-Jones Robert P. , Wood Vincent T.
Published: August 2006

Exact solutions of the Navier–Stokes or Euler equations of motion and the continuity equation in cylindrical coordinates for 3D, axisymmetric, inviscid, or laminar flows are utilized to represent evolving vortices that roughly model tornado cyclones or misocyclones contracting to tornadoes. These solutions are unsteady versions of the diffusive Burgers–Rott vortex and the inviscid Rankine-combined vortex. They satisfy the free-slip condition at the ground. Different vortices are obtained by choosing different values of the constant eddy viscosity and uniform horizontal convergence while holding the circulation at infinity constant. A simulated Weather Surveillance Radar-1988 Doppler (WSR-88D) is employed to generate time-varying Doppler velocity signatures in uniform reflectivity of these analytical vortices at ranges of 25 and 50 km from the radar. Mean Doppler velocities are determined by computing 3D integrals over effective resolution volumes. Magnitudes of Doppler vortex signatures at different times in the evolution of the stationary vortices are computed for effective beamwidths of 1.02° and 1.39°, which correspond to azimuthal sampling intervals of 0.5° and 1.0°, respectively. Four tornado predictors—rotational velocity, shear, excess rotational kinetic energy, and circulation—are examined.

Results of the simulations show that for smaller effective beamwidths, Doppler vortex signatures are stronger and exceed fixed threshold values of rotational velocity and shear earlier. With finer azimuthal resolution, tornado cyclone, misocyclone, or tornado signatures switch to tornadic vortex signatures later. Circulations of the vortex signatures give good estimates of the circulations of the simulated tornadoes and tornado cyclones with relative insensitivity to range, effective beamwidth, and stage of evolution. High circulation and convergence values of a rotation signature reveal the potential for a tornado earlier than all the other predictors, which increase significantly during tornadogenesis.
Ground Clutter Filtering Dual-Polarized, Staggered PRT Sequences
Authors: Sachidananda M. , Zrnic Dusan S.
Published: August 2006

A procedure to filter the ground clutter from a dual-polarized, staggered pulse repetition time (PRT) sequence and recover the complex spectral coefficients of the weather signal is presented. While magnitude spectra are sufficient for estimation of the spectral moments from staggered PRT sequences, computation of differential phase in dual-polarized radars requires recovery of the complex spectra. Herein a method is given to recover the complex spectral coefficients after the ground clutter is filtered. Under the condition of “narrow” spectra, it is possible to recover the differential phase, ΦDP, and the copolar correlation coefficient, ρhv, accurately, in addition to the differential reflectivity, ZDR. The technique is tested on simulated time series and on actual radar data. The efficacy of the method is demonstrated on plan position indicator (PPI) plots of polarimetric variables.
A Radar Simulator for High-Resolution Nonhydrostatic Models
Authors: Caumont Olivier , Ducrocq Véronique , Delrieu Guy , Gosset Marielle , Pinty Jean-Pierre , Parent du Châtelet Jacques , Andrieu Hervé , Lemaître Yvon , Scialom Georges
Published: August 2006

A full radar simulator for high-resolution (1–5 km) nonhydrostatic models has been developed within the research nonhydrostatic mesoscale atmospheric (Meso-NH) model. This simulator is made up of building blocks, each of which describes a particular physical process (scattering, beam bending, etc.). For each of these blocks, several formulations have been implemented. For instance, the radar simulator offers the possibility to choose among Rayleigh, Rayleigh–Gans, Mie, or T-matrix scattering methods, and beam bending can be derived from an effective earth radius or can depend on the vertical gradient of the refractive index of air. Moreover, the radar simulator is fully consistent with the microphysical parameterizations used by the atmospheric numerical model.

Sensitivity experiments were carried out using different configurations for the simulator. They permitted the specification of an observation operator for assimilation of radar reflectivities by high-resolution nonhydrostatic numerical weather prediction systems, as well as for their validation. A study of the flash flood of 8–9 September 2002 in southeastern France, which was well documented with volumetric data from an S-band radar, serves to illustrate the capabilities of the radar simulator as a validation tool for a mesoscale model.
True Along-Track Scan to Improve Radiation Budget Estimations
Authors: Capderou Michel , Viollier Michel
Published: August 2006

Multiangle approaches for radiance-to-flux conversion require accurate coregistration between the observations from nadir- and oblique-viewing directions. The along-track mode of Earth Radiation Budget (ERB) scanning instruments, such as the Clouds and the Earth’s Radiant Energy System (CERES), provides some multiangular observations with almost the same target observed from nadir, aft, and fore directions. To improve the overlaps of multiangle observations, this study explains how to introduce a yaw steering angle in the along-track scan mode so as to reduce the residual collocations errors. The implementation of this correction to the CERES/Terra along-track mode shows that the distances between the nadir and the oblique (55°) observations are reduced from about 40 to 2 km. Both oblique radiances are shown to be equal with small rms differences: 3.9% (all scenes) and 1.8% (homogeneous scenes), compared, respectively, to 7.0% and 3.5% before the scan adjustment.
The Shepherd of Hermas
Authors: Verheyden Joseph
Published: August 2006

The article introduces the reader to some preliminary questions concerning the Shepherd of Hermas, and to key topics of the work: the issue of repentance, its ecclesiology, and the life situation of a socially mixed community, experiencing, or threatened by, enmity from the outside world.
The Foolish Father and the Economics of Grace
Authors: Eastman Susan
Published: August 2006

By both ancient and modern standards, the exemplary father in the Parable of the Prodigal Son is a foolish parent. Nonetheless his foolish actions reveal an economy of grace that opens the door to repentance and reconciliation, by forgiving debts and exercising unaccountable generosity.
To Glean or Not to Glean...
Authors: Baker David L.
Published: August 2006

According to Old Testament law (Lev 19:9-10; 23:22; Deut 24:19-22), harvest leftovers should be reserved for the poor. While gleaning is still practised in some countries, elsewhere it is unwelcome. Yet there are many hungry people today and an urgent need to make agricultural surpluses available to them.
Health Status and the Five-factor Personality Traits in a Nationally Representative Sample
Authors: Goodwin Renee D. , Friedman Howard S.
Published: August 2006

The authors’ objective was to determine the association between the ‘big-five’ personality traits and mental and physical disorders among adults in the United States. The Midlife Development in the United States Survey, a nationally representative sample of 3032 adults ages 25-74, was used to determine the association between the five-factor traits of personality and common mental and physical disorders. Findings are consistent with and extend previous results showing that conscientiousness is associated with significantly reduced likelihood of a wide range of mental and physical disorders among adults in the general population, and inversely that neuroticism is associated with increased rates. Among adults with physical illnesses, associations were found between personality and likelihood of physical limitations, especially conscientiousness. These findings provide a framework upon which research on complex causal processes may proceed. Thus future research attention might profitably be directed to conscientiousness-relevant processes, such as adherence to health and treatment recommendations and internalization of healthy societal norms for sensible health-related behavior.
‘When Suppression Backfires’
Authors: Soetens Barbara , Braet Caroline , Dejonckheere Peter , Roets Arne
Published: August 2006

Based on Wegner’s Ironic Processing Theory, this study examines the effects of suppressing eating-related thoughts in a sample of 77 female students. A distinction was made between disinhibited restrainers (high dietary restraint/high disinhibition), inhibited restrainers (high dietary restraint/low disinhibition) and low restrainers. Results indicate that disinhibited restrainers used thought suppression more often and were the only group to show a rebound effect for eating-related thoughts after suppression. No effects of suppression on willingness and desire to eat emerged. Hence, thought suppression may be counterproductive at least for a subgroup of restrainers and may fuel eating-related preoccupations. More research is required to evaluate effects on eating behaviour.