bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross‐layer design vehicle‐aided handover scheme in VANETs
Authors: Chiu Kuan‐Lin , Hwang Ren‐Hung , Chen Yuh‐Shyan
Published: October 2009

The requirement for in‐vehicle passengers to access Internet multimedia services has risen recently. As a consequence, Vehicle Ad hoc NETwork (VANET) has gained much attention, and is regarded as a promising solution for providing in‐vehicle Internet service through inter‐vehicle and infrastructure communication. A new developed wireless network technique, termed WiMAX Mobile Multihop Relay (MMR), provides a good communication framework for a VANET formed from vehicles on high‐speed freeways. Applying MMR WiMAX allows some public transportation vehicles to act as relay vehicles (RVs) to provide Internet access to passenger vehicles. However, the standard handover procedure of mobile or MMR WiMAX suffers long delay due to the lack of information about the next RV. This study presents a cross‐layer fast handover scheme, called vehicular fast handover scheme (VFHS), where the physical layer information is shared with the MAC layer, to reduce the handover delay. The key idea of VFHS is to utilize oncoming side vehicles (OSVs) to accumulate physical and MAC layers information of passing through RVs and broadcast the information to vehicles that are temporarily disconnected, referred to as disconnected vehicles (DVs). A DV can thus perform a rapid handover when it enters the transmission range of one of approaching RVs. The effectiveness of VFHS is verified using ns2 simulations. Simulation results indicate that VFHS significantly decreases handover latency and packet loss. Copyright © 2009 John Wiley & Sons, Ltd.
Doppler‐shifted frequency measurement based positioning for roadside‐vehicle communication systems
Authors: Xu Bo , Shen Lianfeng , Yan Feng , Zheng Jun
Published: October 2009

Node positioning is a useful service for a vehicular communication system. The global positioning system (GPS) is the most popular positioning technique widely used in vehicular communication systems. However, GPS cannot work effectively in many situations, for example, in a tunnel or under a bridge. For accurate positioning in such situations, it is desirable to have more reliable positioning techniques. In this paper, we propose a novel method for node positioning in vehicular communication systems. Unlike existing positioning methods that employ a roadside node as an observation station, the proposed positioning method allows a vehicular node to play the role of an observation station, and estimates the vehicular node's absolute coordinates based on the measurement of the Doppler frequency shift, the velocity of the vehicular node, and the known absolute coordinates of roadside nodes. To improve positioning accuracy, it introduces extended Kalman filtering (EKF) to mitigate the effects of channel noise and multipath interference. Analytical and simulation results show that the proposed positioning method can significantly improve the positioning accuracy compared with differential GPS and reduce the positioning delay. Copyright © 2009 John Wiley & Sons, Ltd.
Hybrid Hand‐Assisted Colectomy for Transverse Colon Cancer: A Useful Technique for Non‐Expert Laparoscopic Surgeons
Authors: Takakura Yuji , Okajima Masazumi , Yoshimitsu Masanori , Hinoi Takao , Ikeda Satoshi , Ohdan Hideki
Published: October 2009

Background

Laparoscopic assisted colectomy (LAC) is commonly performed, but LAC for transverse colon cancer is a complex procedure, even in the hands of experts. In particular, laparoscopic take‐down of the splenic and/or the hepatic flexure and dissection of the lymph nodes around the middle colic vessels are extremely complicated maneuvers compared to the complexity of these procedures during open surgery. We herein describe a simple and less‐invasive technique for performing hybrid hand‐assisted laparoscopic colectomy (hybrid‐HALC). This procedure combines the established convenient and safe techniques of open surgery with the less invasive hand‐assisted laparoscopic approach.

Methods

From 2000 to 2007, 22 patients with transverse colon cancer underwent hybrid‐HALC at our facility. Short‐term outcomes of hybrid‐HALC were retrospectively compared with those of LAC over the same period and with those of conventional open surgery as a historical control.

Results

The intraoperative and postoperative data indicating the short‐term outcomes of the hybrid‐HALC group were better than those of conventional open surgery and similar to those of the LAC group; the mean operative time for hybrid‐HALC was 40 min shorter than that for LAC. Furthermore, the reduction in the operative time in the hybrid‐HALC group was more prominent in the case of non‐expert surgeons.

Conclusions

We conclude that hybrid‐HALC for transverse colon cancer is a feasible, convenient, and less‐invasive technique, and that it is a useful alternative, especially for non‐expert laparoscopic surgeons.
Accuracy of MRI and 18F‐FDG PET/CT for Restaging After Preoperative Concurrent Chemoradiotherapy for Rectal Cancer
Authors: Cho Yong Beom , Chun Ho‐Kyung , Kim Min Ju , Choi Joon Young , Park Chi‐Min , Kim Byung‐Tae , Lee Soon Jin , Yun Seong Hyeon , Kim Hee Cheol , Lee Woo Yong
Published: October 2009

Background

Performing a restaging work‐up with magnetic resonance imaging (MRI) and 18F‐fluorodeoxyglucose‐positron emission tomography/computed tomography (18F‐FDG PET/CT) can provide information about the effects that are related to preoperative concurrent chemoradiotherapy (CCRT). The purpose of the present study was to investigate the accuracy of MRI and 18F‐FDG PET/CT for restaging after preoperative CCRT for rectal cancer.

Methods

Between April 2005 and February 2006, 30 patients with histologically proven rectal adenocarcinoma were included in this study. Pelvic MRI and 18F‐FDG PET/CT were performed to clinically restage the tumor after CCRT. The results of the pathologic staging were correlated with those of the MRI and 18F‐FDG PET/CT after CCRT. Two patients underwent transanal endoscopic microsurgery after CCRT, and they were excluded when the N category was evaluated.

Results

The overall accuracy of MRI for the T category was 67% (κ = 0.422, P = 0.003), whereas overstaging and understaging occurred in 30 and 3% of the patients, respectively. For the N category, accurate staging was noted in 75% (κ = 0.410, P = 0.030) of all the patients, whereas 14% were overstaged and 11% were understaged. The overall accuracy rates for the T and N categories with performing 18F‐FDG PET/CT were 60% (κ = 0.372, P = 0.004) and 71% (κ = 0.097, P = 0.549), respectively. While MRI could not predict any patient who showed a pathologic complete response, 18F‐FDG PET/CT predicted three of the four patients who showed a pathologic complete response after preoperative CCRT. Furthermore, 18F‐FDG PET/CT identified distant metastases with an accuracy rate of 97%.

Conclusions

For restaging patients with rectal cancer after preoperative CCRT, MRI is a useful diagnostic modality to predict both the T and N categories. 18F‐FDG PET/CT is helpful in predicting a pathologic complete response and in finding metastasis after preoperative CCRT.
Incidental Gallbladder Cancer Diagnosed Following Laparoscopic Cholecystectomy
Authors: Choi Sae Byeol , Han Hyung Joon , Kim Chung Yun , Kim Wan Bae , Song Tae‐Jin , Suh Sung Ock , Kim Young Chul , Choi Sang Yong
Published: October 2009

Background

Laparoscopic cholecystectomy (LC) is the treatment of choice for benign gallbladder disease. Gallbladder cancers have been found following LC. The aim of the present study was to evaluate the survival outcome and prognosis of incidental gallbladder cancer diagnosed after LC.

Methods

From January 2002 to December 2007, 3,145 patients underwent LC at the Department of Surgery, Korea University Medical Center. Of these, 33 patients (1.05%) were diagnosed with gallbladder cancer after LC. Clinicopathological characteristics were retrospectively reviewed in this study.

Results

Of the 33 patients studied, 9 were men and 24 were women. Laparoscopic cholecystectomy alone was performed in 26 patients, and additional radical surgery was performed in 7 others. Regarding tumor staging, there were 2 Tis, 6 T1a, 4 T1b, 17 T2, and 4 T3 tumors. Male patients had a significantly higher incidence of moderately and poorly differentiated tumors (P < 0.001), T2 and T3 tumors (P = 0.02), additional second operations (P = 0.046), and recurrence (P = 0.016). The cumulative 1‐, 3‐, and 5‐year survival rates were 87.2, 73.1, and 47.0%, respectively. Univariate analysis revealed that significant prognostic factors for poorer survival were male gender (P = 0.026), age older than 65 years (P = 0.013), the presence of inflammation (P = 0.009), moderately or poorly differentiated tumor (P < 0.001), nonpolypoid gross type (P = 0.003), and pT stage (P < 0.001). Tumor differentiation was a significantly independent predictor of poor prognosis.

Conclusions

Male patients exhibited aggressive tumor characteristics. Laparoscopic cholecystectomy is an adequate treatment for pT1 tumors. For pT2 and pT3 patients, additional radical surgery might be needed to achieve a tumor‐free surgical margin, along with lymph node dissection.
Lymph Node Harvest in Colon Cancer: Influence of Microsatellite Instability and Proximal Tumor Location
Authors: Søreide Kjetil , Nedrebø Bjørn Steinar , Søreide Jon Arne , Slewa Aida , Kørner Hartwig
Published: October 2009

Background

At least 12 harvested lymph nodes are recommended for proper staging of colon cancer. The effect of tumor‐related factors associated with lymph node harvest is not well understood as data are lacking. We investigated tumor‐related factors in relation to the number of lymph nodes harvested.

Methods

Patient and tumor characteristics were investigated in relation to harvested lymph nodes (LN ≥ 12), number of metastatic nodes, LN ratio (LNR), and prognosis with univariate and multivariate analyses.

Results

An LN harvest ≥12 nodes was achieved in 36% of the patients. Having <12 nodes harvested was not associated with increased risk for locoregional recurrence, distant metastasis, or decreased survival. Tumor size >5 cm, microsatellite instability (MSI), and proximal tumor location predicted a harvest of LN ≥ 12. The highest rate (54%) of LN ≥ 12 was found for MSI cancers [odds ratio (OR) 2.9, 95% confidence interval (CI) 1.3–6.5; P = 0.011]. Multivariate analysis identified a proximal location as an independent factor of LN ≥ 12 (adjusted OR 3.5, 95% CI 1.5–8.2; P = 0.003), with MSI an independent factor in stage II to III colon cancer (adjusted OR 2.6, 95% CI 1.1–6.0; P = 0.026). To determine the best prognosticator, LNR was the only significant factor in the multivariate analysis (Cox proportional hazards) with a hazard ratio (HR) of 2.9 (95% CI 1.1–7.8; P = 0.038) for LNR 0.01–0.17 and an HR of 5.8 (95% CI 2.5–13.1; P < 0.001).

Conclusions

Proximal tumor location and microsatellite instability are associated with a higher number of lymph nodes harvested, pointing to possible underlying genetic and immunologic mechanisms. The LNR is an independent prognostic variable for colon cancer.
Tunable Visible Emission of Ag-Doped CdZnS Alloy Quantum Dots
Authors: Sethi Ruchi , Kumar Lokendra , Sharma Prashant K , Pandey AC
Published: October 2009

Highly luminescent Ag-ion-doped Cd1−xZnxS (0 ≤ x ≤ 1) alloy nanocrystals were successfully synthesized by a novel wet chemical precipitation method. Influence of dopant concentration and the Zn/Cd stoichiometric variations in doped alloy nanocrystals have been investigated. The samples were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) to investigate the size and structure of the as prepared nanocrystals. A shift in LO phonon modes from micro-Raman investigations and the elemental analysis from the energy dispersive X-ray analysis (EDAX) confirms the stoichiometry of the final product. The average crystallite size was found increasing from 1.0 to 1.4 nm with gradual increase in Ag doping. It was observed that photoluminescence (PL) intensity corresponding to Ag impurity (570 nm), relative to the other two bands 480 and 520 nm that originates due to native defects, enhanced and showed slight red shift with increasing silver doping. In addition, decrease in the band gap energy of the doped nanocrystals indicates that the introduction of dopant ion in the host material influence the particle size of the nanocrystals. The composition dependent bandgap engineering in CdZnS:Ag was achieved to attain the deliberate color tunability and demonstrated successfully, which are potentially important for white light generation.
Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface
Authors: Lin Xiu-Zhu , Li Jing , Wu Qi-Hui
Published: October 2009

The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface.
Compactly supported analytic indices for Lie groupoids
Authors: Carrillo Rouse Paulo
Published: October 2009

For any Lie groupoid we construct an analytic index morphism taking values in a modified K-theory group which involves the convolution algebra of compactly supported smooth functions over the groupoid. The construction is performed by using the deformation algebra of smooth functions over the tangent groupoid constructed in [CR06]. This allows us in particular to prove a more primitive version of the Connes-Skandalis longitudinal index theorem for foliations, that is, an index theorem taking values in a group which pairs with cyclic cocycles. As another application, forDa-PDO elliptic operator with associated indexindwe prove that the pairing

with τ a bounded continuous cyclic cocycle, only depends on the principal symbol class [σ(D)]∈K0. The result is completely general for étale groupoids. We discuss some potential applications to the Novikov conjecture.
Twisted cyclic theory and an index theory for the gauge invariant KMS state on the Cuntz algebra On
Authors: Carey A.L. , Phillips J. , Rennie A.
Published: October 2009

This paper presents, by example, an index theory appropriate to algebras without trace. Whilst we work exclusively with Cuntz algebras the exposition is designed to indicate how to develop a general theory. Our main result is an index theorem (formulated in terms of spectral flow) using a twisted cyclic cocycle where the twisting comes from the modular automorphism group for the canonical gauge action on each Cuntz algebra. We introduce a modified K1-group for each Cuntz algebra which has an index pairing with this twisted cocycle. This index pairing for Cuntz algebras has an interpretation in terms of Araki's notion of relative entropy.
Food, energy and macronutrient contribution of out-of-home foods in school-going adolescents in Cotonou, Benin
Authors: Nago Eunice S. , Lachat Carl K. , Huybregts Lieven , Roberfroid Dominique , Dossa Romain A. , Kolsteren Patrick W.
Published: October 2009

The objective of the present study was to document the food, energy and macronutrient contribution of out-of-home prepared foods in school-going adolescents in Cotonou (Benin) and compare the food, energy and macronutrient intakes of low and high out-of-home consumers. We used a cross-sectional study with 24 h dietary recalls on two non-consecutive school days to collect food intake data. Low and high consumers were defined respectively as subjects whose percentage of daily energy intake from out-of-home foods was in the first and the third terciles of the sample distribution. The setting was twelve secondary schools in Cotonou with 656 adolescents aged 13–19 years. Out-of-home prepared foods contributed more than 40 % of the daily energy, fat, protein, carbohydrate and fibre intakes and of the daily weight of food in the adolescents. They were highly present at breakfast and as afternoon snacks in high consumers, providing respectively 94 and 82 % of the energy intake of high consumers at breakfast and as afternoon snacks. Low consumers ate more fruit and vegetables and cereal grain products than high consumers whereas high consumers consumed more sweet energy-dense foods. Both categories had a diet poor in fruit and vegetables (hardly one-fourth of the recommended 400 g) and high in fat. We concluded that out-of-home foods are important in the diet of urban school adolescents in Benin. Therefore, they should be investigated in depth and taken into account in the development of interventions to promote healthy diet and lifestyles in adolescents.
Chronic intake of a high-cholesterol diet resulted in hepatic steatosis, focal nodular hyperplasia and fibrosis in non-obese mice
Authors: Sumiyoshi Maho , Sakanaka Masahiro , Kimura Yoshiyuki
Published: October 2009

We investigated the effects of a high-cholesterol (HC) diet administered long term (25 or 55 weeks) on metabolic disorders including hepatic damage in mice. The mice were fed the HC diet (15 % milk fat, 1·5 % cholesterol and 0·1 % cholic acid, w/w) for 25 or 55 weeks. Body and adipose tissue weights were similar to those of mice fed a control diet. Consumption of the HC diet long term resulted in hypercholesterolaemia, hepatic steatosis and gallstones. In addition, focal nodular hyperplasia (FNH) and mild fibrosis of the liver developed in all mice fed the HC diet for 55 weeks. Plasma levels of monocyte chemoattractant protein (MCP)-1 were elevated, and the level of hepatic platelet-derived growth factor (PDGF)-B protein was increased in mice fed the HC diet compared with those fed the control diet. Thus, it seems likely that the liver fibrosis and FNH caused by the long-term consumption of a HC diet may be partly due to an elevation of plasma MCP-1 and hepatic PDGF expression.
The effect of a fissure on storage in a porous medium
Authors: NEUFELD JEROME A. , VELLA DOMINIC , HUPPERT HERBERT E.
Published: October 2009

We consider the two-dimensional buoyancy driven flow of a fluid injected into a saturated semi-infinite porous medium bounded by a horizontal barrier in which a single line sink, representing a fissure some distance from the point of injection, allows leakage of buoyant fluid. Our studies are motivated by the geological sequestration of carbon dioxide (CO2) and the possibility that fissures in the cap rock may compromise the safe long-term storage of CO2. A theoretical model is presented that accounts for leakage through the fissure using two parameters, which characterize leakage driven both by the hydrostatic pressure within the overriding fluid and by the buoyancy of the fluid within the fissure. We determine numerical solutions for the evolution of both the gravity current within the porous medium and the volume of fluid that has escaped through the fissure as a function of time. A quantity of considerable practical interest is the efficiency of storage, which we define as the amount of fluid remaining in the porous medium relative to the amount injected. This efficiency scales like t−1/2 at late times, indicating that the efficiency of storage ultimately tends to zero. We confirm the results of our model by comparison with an analogue laboratory experiment and discuss the implications of our two-dimensional model of leakage from a fissure for the geological sequestration of CO2.
A twin study of specific bulimia nervosa symptoms
Authors: Mazzeo S. E. , Mitchell K. S. , Bulik C. M. , Aggen S. H. , Kendler K. S. , Neale M. C.
Published: October 2009

Background

Twin studies have suggested that additive genetic factors significantly contribute to liability to bulimia nervosa (BN). However, the diagnostic criteria for BN remain controversial. In this study, an item-factor model was used to examine the BN diagnostic criteria and the genetic and environmental contributions to BN in a population-based twin sample. The validity of the equal environment assumption (EEA) for BN was also tested.

Method

Participants were 1024 female twins (MZn=614, DZn=410) from the population-based Mid-Atlantic Twin Registry. BN was assessed using symptom-level (self-report) items consistent with DSM-IV and ICD-10 diagnostic criteria. Items assessing BN were included in an item-factor model. The EEA was measured by items assessing similarity of childhood and adolescent environment, which have demonstrated construct validity. Scores on the EEA factor were used to specify the degree to which twins shared environmental experiences in this model.

Results

The EEA was not violated for BN. Modeling results indicated that the majority of the variance in BN was due to additive genetic factors. There was substantial variability in additive genetic and environmental contributions to specific BN symptoms. Most notably, vomiting was very strongly influenced by additive genetic factors, while other symptoms were much less heritable, including the influence of weight on self-evaluation. These results highlight the importance of assessing eating disorders at the symptom level.

Conclusions

Refinement of eating disorder phenotypes could ultimately lead to improvements in treatment and targeted prevention, by clarifying sources of variation for specific components of symptomatology.
The neuropsychology of the schizo-obsessive subtype of schizophrenia: a new analysis
Authors: Patel D. D. , Laws K. R. , Padhi A. , Farrow J. M. , Mukhopadhaya K. , Krishnaiah R. , Fineberg N. A.
Published: October 2009

Background

Interest in the neuro-cognitive profile of patients with schizophrenia and co-morbid obsessive compulsive disorder (schizo-OCD) is rising in response to reports of high co-morbidity rates. Whereas schizophrenia has been associated with global impairment in a wide range of neuro-cognitive domains, OCD is associated with specific deficits featuring impaired performance on tasks of motor and cognitive inhibition involving frontostriatal neuro-circuitry.

Method

We compared cognitive function using the CANTAB battery in patients with schizo-OCD (n=12) and a schizophrenia group without OCD symptoms (n=16). The groups were matched for IQ, gender, age, medication, and duration of illness.

Results

The schizo-OCD patients made significantly more errors on a task of attentional set-shifting (ID-ED set-shift task). By contrast, no significant differences emerged on the Stockings of Cambridge task, the Cambridge Gamble Task or the Affective Go/NoGo tasks. No correlation emerged between ID-ED performance and severity of schizophrenia, OCD or depressive symptoms, consistent with neurocognitive impairment holding trait rather than state-marker status. Schizo-obsessives also exhibited a trend toward more motor tics emphasizing a neurological contribution to the disorder.

Conclusion

Our findings reveal a more severe attentional set-shifting deficit and neurological abnormality that may be fundamental to the neuro-cognitive profile of schizo-OCD. The clinical implications of these impairments merit further exploration in larger studies.
Impaired probabilistic reversal learning in youths with mood and anxiety disorders
Authors: Dickstein D. P. , Finger E. C. , Brotman M. A. , Rich B. A. , Pine D. S. , Blair J. R. , Leibenluft E.
Published: October 2009

Background

From an affective neuroscience perspective, our understanding of psychiatric illness may be advanced by neuropsychological test paradigms probing emotional processes. Reversal learning is one such process, whereby subjects must first acquire stimulus/reward and stimulus/punishment associations through trial and error and then reverse them. We sought to determine the specificity of previously demonstrated reversal learning impairments in youths with bipolar disorder (BD) by now comparing BD youths to those with severe mood dysregulation (SMD), major depressive disorder (MDD), anxiety (ANX), and healthy controls.

Method

We administered the probabilistic response reversal (PRR) task to 165 pediatric participants aged 7–17 years with BD (n=35), SMD (n=35), ANX (n=42), MDD (n=18) and normal controls (NC; n=35). Our primary analysis compared PRR performance across all five groups matched for age, sex and IQ.

Results

Compared to typically developing controls, probabilistic reversal learning was impaired in BD youths, with a trend in those with MDD (p=0.07).

Conclusions

Our results suggest that reversal learning deficits are present in youths with BD and possibly those with MDD. Further work is necessary to elucidate the specificity of neural mechanisms underlying such behavioral deficits.
Surveillance forListeria monocytogenesand listeriosis, 1995–2004
Authors: CLARK C. G. , FARBER J. , PAGOTTO F. , CIAMPA N. , DORÉ K. , NADON C. , BERNARD K. , NG L.-K.
Published: October 2009

Canadian cases and outbreaks of illness caused byListeria monocytogenesbetween 1995 and 2004 were assessed. Isolates (722 total) were characterized by serotyping, and pulsed-field gel electrophoresis (PFGE) was performed to provide a means of detecting case clusters. Rates of listeriosis remained fairly consistent during the period of study, and patient characteristics were similar to those seen in studies of other populations. Most isolates were obtained from blood and cerebrospinal fluid, although during some outbreak investigations isolates were also obtained from stools. Serotype 1/2a predominated in isolates from patients in Canada, followed by serotypes 4b and 1/2b. Outbreaks caused byL. monocytogenesthat occurred during the period of study were caused by isolates with serotypes 1/2a and 4b. A retrospective analysis of PFGE data uncovered several clusters that might have represented undetected outbreaks, suggesting that comprehensive prospective PFGE analysis coupled with prompt epidemiological investigations might lead to improved outbreak detection and control.
DIAGNOSIS AND MANAGEMENT OF SELECTIVE FETAL GROWTH RESTRICTION IN MONOCHORIONIC TWINS
Authors: GRATACÓS EDUARD , EIXARCH ELISENDA , CRISPI FATIMA
Published: October 2009

Selective fetal growth restriction (sFGR) has been reported to occur in about 10–15% of monochorionic (MC) twins. The diagnosis of sFGR has been based on variable criteria including estimated fetal weight (EFW), abdominal circumference and/or the degree of fetal weight discordance. Recent studies tend to use a simple definition which includes the presence of an EFW less than the 10th percentile in the smaller twin. Some would argue that the intertwin fetal weight discordance should be included in the definition. Indeed this factor plays a major role in the complications presented by these cases. While the majority of cases with one fetus below the 10th percentile usually will also present with a large intertwin EFW discordance, the contrary is not always true. Thus, it is possible to find MC twins with remarkable intertwin EFW discordance but the EFW of both fetuses are still within normal ranges. Although it appears to be common sense that a large intertwin discrepancy might represent a higher risk for some of the complications described later in this review, there is no consistent evidence to support this notion. Therefore, due to its simplicity, a definition based on an EFW below 10th percentile in one twin is probably the most useful for clinical and research purposes.
Measured electric and magnetic fields from an unusual cloud‐to‐ground lightning flash containing two positive strokes followed by four negative strokes
Authors: Jerauld J. E. , Uman M. A. , Rakov V. A. , Rambo K. J. , Jordan D. M. , Schnetzer G. H.
Published: October 2009

We present electric and magnetic fields measured at multiple stations between about 300 and 800 m of a cloud‐to‐ground “bipolar” lightning flash containing two initial positive strokes, separated in time by 53 ms and striking ground at two locations separated by about 800 m, followed by four negative strokes that traversed the same path as the second positive stroke. The leader electric field durations for the positive first, positive second, and negative third strokes were about 120 ms, 35 ms, and 1 ms, respectively. The first‐stroke leader electric field changes measured at five stations ranged from about +16 to +35 kV/m, the second stroke +8 to +13 kV/m, and the third stroke −0.9 to −1.8 kV/m (atmospheric electricity sign convention). The microsecond‐scale return stroke waveforms of the first and second (positive) strokes exhibited a similar “slow‐front/fast‐transition” to those observed for close negative first strokes. The peak rate‐of‐change of the positive first stroke electric field normalized to 100 km was about 20 V m−1μs−1, similar to the values observed for close negative first strokes. The positive second stroke was followed by a long continuing current of duration at least 400 ms, while the positive first stroke had a total current duration of only about 1 ms. All four negative strokes were followed by long continuing current, with durations ranging from about 70 ms to about 230 ms. The overall flash duration was about 1.5 s.
Bayesian inversion for facies detection: An extensible level set framework
Authors: Cardiff M. , Kitanidis P. K.
Published: October 2009

In many cases, it has been assumed that the variability in hydrologic parameters can be adequately described through a simple geostatistical model with a given variogram. In other cases, variability may be best described as a series of “jumps” in parameter behavior, e.g., those that occur at geologic facies contacts. When using indirect measurements such as pump tests to try to map such heterogeneity (during inverse modeling), the resulting images of the subsurface are always affected by the assumptions invoked. In this paper, we discuss inversion for parameter fields where prior information has suggested that major variability can be described by boundaries between geologic units or facies. In order to identify such parameter fields, we propose a Bayesian level set inversion protocol framework, which allows for flexible zones of any shape, size, and number. We review formulas for defining facies locations using the level set method and for moving the boundaries between zones using a gradient‐based technique that improves fit through iterative deformation of the boundaries. We describe the optimization algorithm employed when multiple level set functions are used to represent a field with more than two facies. We extend these formulas to the investigation of the inverse problem in a Bayesian context in which prior information is taken into account and through which measures of uncertainty can be derived. We also demonstrate that the level set method is well suited for joint inversion problems and present a strategy for integrating different data types (such as hydrologic and geophysical) without assuming strict petrophysical relations. Our framework for joint inversion also contrasts with many previous methods in that all data sources (e.g., both hydrologic and geophysical) contribute to boundary delineation at once.
Deformation modes of subducted lithosphere at the core‐mantle boundary: An experimental investigation
Authors: Loubet N. , Ribe N. M. , Gamblin Y.
Published: October 2009

Ancient subducted lithosphere may be an important source of the seismically observed heterogeneity and anisotropy in the D″ layer. Proper interpretation of the seismic observations therefore requires an understanding of how subducted lithosphere deforms upon reaching the core‐mantle boundary (CMB). Here we study this process experimentally, using an analog model system in which a sheet of viscous sugar syrup (representing the subducted lithosphere) falls vertically onto an impermeable surface (the “CMB”) at the bottom of a reservoir of less viscous syrup (the “ambient mantle”). For sheet/ambient viscosity contrasts γ less than a critical value γc that depends on the ratio of the fall height to the sheet thickness, the sheet impinges on the CMB as a stagnation flow with bilateral symmetry. For γ > γc, however, the sheet undergoes a periodic folding instability. We determine experimentally a universal scaling law for the folding amplitude δ as a function of the viscosities and densities of the two fluids and the thickness and vertical velocity of the sheet where it enters the folding region. To apply this law to the Earth, we assume that the sheet's excess viscosity and density relative to the ambient mantle are both controlled by the same temperature anomaly ΔT. Using estimated rheological parameters for diffusion creep in the lowermost mantle, we find that the folding criterion γ > γc requires ΔT > 300 K. The presence of folded lithosphere at the CMB beneath the Cocos plate, suggested recently on the basis of seismic data by Hutko et al. [2006], is unlikely to be the result of in situ folding because the temperature anomaly (400–700 K) required to explain the observed variations in the depth of the postperovskite phase transition is probably too large to be preserved in a deeply penetrating slab. However, the seismic observations might be explained in an alternative way by a “pile” of folded lithosphere that formed at 660 km depth and subsequently sank to the CMB.
Characterizing the seismogenic zone of a major plate boundary subduction thrust: Hikurangi Margin, New Zealand
Authors: Wallace Laura M. , Reyners Martin , Cochran Ursula , Bannister Stephen , Barnes Philip M. , Berryman Kelvin , Downes Gaye , Eberhart‐Phillips Donna , Fagereng Ake , Ellis Susan , Nicol Andrew , McCaffrey Robert , Beavan R. John , Henrys Stuart , Sutherland Rupert , Barker Daniel H. N. , Litchfield Nicola , Townend John , Robinson Russell , Bell Rebecca , Wilson Kate , Power William
Published: October 2009

The Hikurangi subduction margin, New Zealand, has not experienced any significant (>Mw 7.2) subduction interface earthquakes since historical records began ∼170 years ago. Geological data in parts of the North Island provide evidence for possible prehistoric great subduction earthquakes. Determining the seismogenic potential of the subduction interface, and possible resulting tsunami, is critical for estimating seismic hazard in the North Island of New Zealand. Despite the lack of confirmed historical interface events, recent geodetic and seismological results reveal that a large area of the interface is interseismically coupled, along which stress could be released in great earthquakes. We review existing geophysical and geological data in order to characterize the seismogenic zone of the Hikurangi subduction interface. Deep interseismic coupling of the southern portion of the Hikurangi interface is well defined by interpretation of GPS velocities, the locations of slow slip events, and the hypocenters of moderate to large historical earthquakes. Interseismic coupling is shallower on the northern and central portion of the Hikurangi subduction thrust. The spatial extent of the likely seismogenic zone at the Hikurangi margin cannot be easily explained by one or two simple parameters. Instead, a complex interplay between upper and lower plate structure, subducting sediment, thermal effects, regional tectonic stress regime, and fluid pressures probably controls the extent of the subduction thrust's seismogenic zone.
In situ measurements of saltwater flux through tidal passes of Lake Pontchartrain estuary by Hurricanes Gustav and Ike in September 2008
Authors: Li Chunyan , Weeks Eddie , Rego Joao L.
Published: October 2009

Storm surge induced saltwater flux through multiple inlets has never been documented. This article reports in situ measurements of saltwater flux through major tidal passes by two consecutive storm surges impacting Lake Pontchartrain estuary in Louisiana during the first two weeks in September 2008. The main peak of inward saltwater flux lasted for 1.9 days during the flood, followed by more than 8 days of outward salt flux. The salt flux rate reached close to 200 tons/sec through the northern channel and 16 tons/sec through the southern channel. Outward flux of salt during Gustav amounted to more than 16 million tons during the receding stage, more than twice of that measured for the flux into the lake. Apparently, overland inundation, which was not measured, caused this biased estimate of influx of salt. Hurricane Ike, however, did not cause such a dramatic difference in influx and outflux of salt.
Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE
Authors: Velicogna I.
Published: October 2009

We use monthly measurements of time‐variable gravity from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission to determine the ice mass‐loss for the Greenland and Antarctic Ice Sheets during the period between April 2002 and February 2009. We find that during this time period the mass loss of the ice sheets is not a constant, but accelerating with time, i.e., that the GRACE observations are better represented by a quadratic trend than by a linear one, implying that the ice sheets contribution to sea level becomes larger with time. In Greenland, the mass loss increased from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009, i.e., an acceleration of −30 ± 11 Gt/yr2 in 2002–2009. In Antarctica the mass loss increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006–2009, i.e., an acceleration of −26 ± 14 Gt/yr2 in 2002–2009. The observed acceleration in ice sheet mass loss helps reconcile GRACE ice mass estimates obtained for different time periods.
Equilibration and variability in a Last Glacial Maximum climate simulation with CCSM3
Authors: Brandefelt J. , Otto‐Bliesner B. L.
Published: October 2009

We present results from a 1862 year simulation of the Last Glacial Maximum (LGM) with the Community Climate System Model version 3 (CCSM3). A quasi steady state is reached after approximately 100 years of integration when the initial cooling trend in the annual global mean atmospheric surface temperature (Ts) levels off and even reverses. After another 150 years of integration the climate continues to cool and reaches a new equilibrium after a total of 800 years of integration. The cause of the continued adjustment of the climate to LGM forcing and boundary conditions is found in the abyssal ocean which is cooling at a rate decreasing from 0.15°C per century until the new equilibrium is reached. The new equilibrium differs substantially from the first quasi steady state with 1.1°C colder global mean Ts and regional differences of 5–15°C in the North Atlantic region and a 30% reduction of the strength of the Atlantic meridional overturning circulation (AMOC). Further, the variability in the global mean Ts is significantly larger in the new equilibrium. This variability is associated with coupled ocean–atmosphere–sea ice variations in the North Atlantic region.
Stormtime measurements of topside ionospheric upflow from Defense Meteorological Satellite Program
Authors: Coley W. R. , Heelis R. A.
Published: October 2009

We have examined characteristics of the vertical ion flux of thermal O+ in the topside high‐latitude ionosphere before and during a number of geomagnetic storms, including the October and November 2003 events, using measurements of the vertical ion drift and ion number density made by the DMSP F13 and F15 spacecraft. Prior to storm onset typical upward fluxes of approximately 108–109 cm−2 s−1 are observed in the auroral zones with somewhat smaller downward fluxes in the polar caps. Immediately following storm onset upward fluxes reach and sometimes exceed 1010 cm−2 s−1 and are observed with vertical velocities of 500–1500 m s−1. At the same time, downward fluxes at the higher latitudes reach unusually high values of 109 cm−2 s−1. Separately integrating the upward and downward fluxes over the high‐latitude region (auroral zone and polar cap) for each spacecraft pass allows the observation of variations in the total upflow/downflow during the progression of a geomagnetic storm. A superposed epoch analysis of events from 1995 to 2004 reveals a pattern of sudden onset of upward flux (averaging approximately 14 hours) with a gradually increasing and more extended period of downward flux (lasting about 24 hours). The upward fluxes are stronger when the coincident fluctuations in the z component of the IMF are larger. Strong upward flux events during storm times tend to occur when the solar wind velocity is elevated and the solar wind density is high. Upward flux events can also occur without a coincident geomagnetic storm if the solar wind velocity is above average.
Photoelectrons as a tool to evaluate spectral variations in solar EUV irradiance over solar cycle timescales
Authors: Peterson W. K. , Stavros E. N. , Richards P. G. , Chamberlin P. C. , Woods T. N. , Bailey S. M. , Solomon S. C.
Published: October 2009

There is limited information about the relative magnitude of the spectral variations in the ionizing component of solar irradiance on solar cycle timescales. We found that the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED)/Solar Extreme Ultraviolet Experiment (SEE) Version 9 irradiance values predict relatively more ionospheric heating at solar minimum than those from Version 8. These changes have direct impacts on solar cycle timescale variations in ionospheric and thermospheric energy inputs derived from them. Photoelectron observations from the Fast Auroral Snapshot (FAST) satellite obtained from 2002 to 2008 are used with solar irradiance data, photoelectron flux models, and models of solar irradiance to examine the solar cycle variations of irradiance in the 4–27 nm range derived from the XPS sensor in the TIMED/SEE instrument suite. Good (±50%) agreement is found between daily photoelectron observations and model predictions. The largest differences between observed and modeled fluxes are in the 4–10 nm range, where the Fast Auroral Snapshot data show that the SEE Version 9 irradiances are systematically low. Our analysis suggests that variation on solar cycle timescales in the TIMED/SEE Version 9 and Flare Irradiance Spectral Model irradiance derived from them are systematically low in the 18–27 nm region. Because of uncertainties in the absolute value of the observed photoelectron fluxes and solar irradiances, differences between observed and modeled photoelectron fluxes are not sufficient to determine more exactly the magnitude of variation on solar cycle timescales of solar irradiance in the 4–27 nm region. These suggestions can be confirmed by higher spectral resolution observations that will be made on the Solar Dynamics Observatory mission.
Apparent stability of GPS monumentation from short‐baseline time series
Authors: King Matt A. , Williams Simon D. P.
Published: October 2009

Long‐running, short (≪1 km) GPS baselines offer an insight into the accuracy budget of geophysical estimates inferred from GPS coordinate time series. In this paper, we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length. Annual signals with amplitude >0.5 mm are evident in various coordinate components at 6 of the 10 sites, with amplitudes exceeding 2.5 mm on two baselines. These signals are largely invariant to elevation cutoff angle. Multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods. They are therefore likely real monument motions, although linear thermal expansion is negligible at most sites. Linear trends >0.25 mm yr−1are evident on four baselines in at least one coordinate component. Subdaily signals are present at all sites at ∼K1 and its higher harmonics. Time‐correlated noise, possibly in the form of flicker noise, dominates despite many common signals being eliminated as a result of the small baseline lengths, although it is around 1 order of magnitude smaller than for single site PPP solutions. We constrain monument random walk motion to be no more than 0.5 mm yr−1/2. If these baseline motion results were representative of the ∼300 currently active IGS sites, 180 would have annual signals >0.5 mm in at least one coordinate component, 120 would have linear rates >0.25 mm yr−1, and almost all sites would have subdaily (K1, K2) signals of >0.1 mm, each solely due to local site effects.
Basin‐scale pCO2 maps estimated from ARGO float data: A model study
Authors: Friedrich T. , Oschlies A.
Published: October 2009

A novel method for mapping surface pCO2 on a basin scale using ARGO floats is presented and tested in the framework of an eddy‐resolving biogeochemical model of the North Atlantic. Voluntary observing ship (VOS) and ARGO float coverage of the year 2005 is applied to the model to generate synthetic “observations.” The model‐generated VOS line “observations” of pCO2, SST, and SSS form a training data set for a self‐organizing neural network. The trained neural network is subsequently applied locally to estimate pCO2 from the model‐generated ARGO float SST and SSS data. The local pCO2 estimates at the simulated float positions are extrapolated using objective mapping. The accuracy of the nearly basinwide pCO2 estimates is assessed by comparing against the pCO2 output of the model that serves as synthetic “ground truth.” For an ARGO float coverage of the year 2005, the resulting monthly mean pCO2 maps cover 70% of the considered area (15°N to 65°N) with an RMS error of 15.9 μatm. Compared to remote sensing‐based estimates that suffer from large regional gaps in optical satellite data coverage, the RMS error in reproducing the annual cycle of pCO2 can be reduced by 42% when the more evenly distributed ARGO float‐based data are used.