bluuebunny/crossref_metadata_2025 huggingface dataset:
Perfluorocarbons as gas transporters for O2, NO, CO and volatile anesthetics
Authors: CABRALES PEDRO , VÁZQUEZ BEATRIZ Y. SALAZAR , NEGRETE ADOLFO CHÁVEZ , INTAGLIETTA MARCOS
Published: February 2008

Perfluorocarbons (PFCs) developed for the intravascular transport of oxygen have a higher solubility for gases compared to plasma and therefore can be used to transport and deliver a variety of bioactive gases for therapeutic purposes. Intravenous infusion of PFCs preequilibrated with carbon monoxide gas may provide a means to produce vasodilatation. A similar effect can be obtained by preloading PFC emulsions with nitric oxide (NO), as well as introducing unsaturated PFC emulsions in the circulation, since these can scavenge and redistribute NO. Volatile anesthetics delivered in conjunction with the intravenous presence of PFCs are more effective at lower dosages, and provide for a more uniform anesthetic effect in terms of duration of anesthesia. PFC emulsions are therefore proposed as vehicles for the transport and delivery of gases to the tissues, offering high accuracy of dosage, and avoiding uncertainties of gas delivery associated with gas inspiration via the lungs.
Resuscitation from hemorrhagic shock: recovery of oxygen carrying capacity or perfusion? Efficacy of new plasma expanders
Authors: TSAI AMY G. , CABRALES PEDRO , ACHARYA SEETHARAMA A. , INTAGLIETTA MARCOS
Published: February 2008

Potential shortages and perceived issues with the biosafety of blood have strengthened interest in the search for alternatives to blood. Currently available plasma expanders are effective in recovering pressure by volume expansion but are not safely deployed beyond the transfusion trigger. Conventional reasoning indicates that this limitation relates to oxygen carrying capacity reaching the threshold where it no longer can satisfy the metabolic demand of the organism; however, recent findings show that this limitation is also determined by other physical factors such as their viscosity and colloidal osmotic pressure. These fluid transport properties have a strong influence on the maintenance of microvascular perfusion and function in conditions of extreme hemodilution that obtain when resuscitation is continued beyond the transfusion trigger with plasma expanders. This realization leads to the possibility of developing new plasma expanders whose physical properties enhance microvascular function compensating for the decreased intrinsic oxygen carrying capacity in extreme hemodilution via enhanced microvascular perfusion. This review presents experimental, systemic and microvascular findings obtained using polyethylene glycol conjugated albumin solutions in extreme hemodilution and shock resuscitation in the hamster window chamber model, concluding that plasma expanders of this type can be effectively used beyond the transfusion trigger.
Solution to the problems of acellular hemoglobins by encapsulation and the intrinsic issues of hemoglobin vesicles as a molecular assembly
Authors: SAKAI HIROMI , SOU KEITARO , TSUCHIDA EISHUN
Published: February 2008

Hemoglobin vesicles (HbV), or liposome‐encapsulated hemoglobins, are developed as artificial oxygen carriers for the use as a transfusion alternative. The safety and efficacy of HbV have been clarified in detail: HbV can overcome the side effects of hemoglobin (Hb) molecules (stroma‐free, and intra‐ or intermolecularly crosslinked) such as vasoconstriction, hypertension and possible vascular damage induced by direct contact of the vascular surface with Hb. On the other hand, intrinsic issues related to the suspension of HbV as a molecular assembly have to be considered: blood compatibility, structural and dispersion stabilities of the vesicles, and the requirement of prompt degradation in the reticuloendothelial system. Having overcome these issues, the results make us confident in advancing further development of HbV. Easy manipulation of physicochemical parameters of HbV provides possibilities for various clinical applications in addition to their use as a transfusion alternative.
Modulation of the polyethylene glycol‐hemoglobin structure to increase the efficiency of plasma expansion and O2 carrying capacity
Authors: ACHARYA SEETHARAMA A. , INTAGLIETTA MARCOS , TSAI AMY G.
Published: February 2008

Polyethylene glycol (PEG) surface decoration of hemoglobin (Hb) is being developed as a design strategy for generating an oxygen carrier with optimal plasma expansion characteristics and maintenance of microvascular function. HexaPEGylated Hb using six copies of 5 kDa PEG provides excellent tissue perfusion when used to correct blood volume losses at a plasma concentration of 2 g Hb/dL (as compared with unPEGylated Hbs used at 6–9 g Hb/dL). Efficacy attained with limited concentration of Hb allows effective use of available Hb obtained from outdated blood. However, the high oxygen affinity of PEG‐Hb in combination with its low plasma concentration limits the effective oxygen delivery capacity, impacting tissue oxygenation. This problem can be remedied either by lowering oxygen affinity of PEG‐Hb or by increasing its concentration in the circulation. PEGylation of low oxygen affinity intramolecularly cross‐linked Hbs, for example αα‐fumaryl‐Hb, lowers oxygen affinity and modulating the pattern of PEGylation (size and number of PEG‐chains to lower the colloidal osmotic pressure of PEG‐Hb) reduces the tendency to dilute the PEG‐Hb concentration in circulation because of fluid shifts into the intravascular volume. Novel chemistry platforms for PEGylation set the stage for next generation lower oxygen affinity PEGylated Hbs that optimizes oxygen delivery and tissue perfusion.
Reactivity in Micelles - Are We Really Able to Design Micellar Catalysts?
Authors: Jurok Radek , Svobodová Eva , Cibulka Radek , Hampl František
Published: February 2008

Coordination of lipophilic alkyl pyridin-2-yl ketoximes 1 to Ni2+ ions, reduction of lipophilic 3-alkoxyacetophenones 2 with sodium borohydride, and alkaline hydrolysis of 4-nitrophenyl diphenyl phosphate (PNPDPP) were employed as probes in the investigation which factors may influence the reactivity of organic compounds in micellar systems. In all these reactions, a lipophilic substrate solubilized in micellar core was attacked by a hydrophilic reagent from the bulk aqueous phase. To evaluate the contribution of electrostatic interactions between the micellar surface charge and the reagent to the observed reactivity, we combined reactions involving the reagents with opposite polarity (Ni2+ cations and borohydride or hydroxide anions) with positively charged micelles of hexadecyltrimethylammonium chloride (CTAC) or bromide (CTAB) and negatively charged micelles of sodium dodecyl sulfate (SDS). Non-ionic micelles (Triton X-100 or Brij 35) served as a reference. The results of the kinetic studies give evidence that each of the investigated systems has unique properties going in particular aspects beyond the scope of the generally accepted concepts of reactivity in micelles.
ANTIHYPERON POLARIZATION IN HIGH-ENERGY INCLUSIVE PROCESSES
Authors: BARROS C. C. , HAMA Y.
Published: February 2008

We propose a model for the antihyperon polarization in high-energy proton-nucleus inclusive reactions, based on the final-state interactions between the antihyperons and other produced particles (predominantly pions). To formulate this idea, we use the previously obtained low-energy pion-(anti-)hyperon interaction using effective chiral Lagrangians, and a hydrodynamic parametrization of the background matter, which expands and decouples at a certain freezeout temperature.1.
MEASUREMENT AND ANALYSIS OF EXCITATION FUNCTIONS AND FORWARD RECOIL RANGE DISTRIBUTIONS IN 12C + 59Co SYSTEM
Authors: AGARWAL AVINASH , RIZVI I. A. , KUMAR RAKESH , YOGI B. K. , CHAUBEY A. K.
Published: February 2008

With the motivation of studying complete and incomplete fusion reactions in a 12 C +59 Co projectile target system, the excitation functions for ( C , p3n ), ( C , 2p2n ), ( C , αn ), ( C , α2n ), ( C , αp3n ) and ( C , 2α2n ) reactions have been measured up to 80 MeV. The well-known activation technique followed by offline high purity Ge γ-ray spectroscopy was used. The measured experimental values were compared with the statistical model calculations by using the ALICE-91 and CASCADE codes. For the calculations obtained by CASCADE, the variation of parameter Fθ, which is the ratio of actual moment of inertia to the rigid body value have also been studied. Considerable enhancement of the measured excitation functions compared to theoretical predictions for some channels clearly indicates the presence of incomplete fusion with complete fusion in the present projectile energy range. The measurements of forward recoil range distribution of evaporation residues at 80 MeV projectile energy confirm these observations.
NEW HADRON STATES
Authors: ZHU SHI-LIN
Published: February 2008

In the past four years we have witnessed the renaissance of the hadron spectroscopy. Many interesting new hadron states were discovered experimentally, some of which do not fit into the quark model easily. I will give a concise overview of these states and their possible interpretations. Topics covered in this review are: (1) candidates of new light hadrons including [Formula: see text] threshold enhancement, X(1835), X(1576), f0(1810), recent candidates of the 1-+ exotic mesons, Y(2175), [Formula: see text] threshold enhancement etc. (2) charmed mesons including p-wave non-strange charmed mesons, Dsj(2317) and Dsj(2460), recent candidates of higher excited charmed mesons, Dsj(2632) etc. (3) charmonium and charmonium-like states such as X(3872), Y(4260), X(3940), Y(3940), Z(3930) etc. The effect from the nearby S-wave open channels on the quark model spectrum above or near strong decay threshold is emphasized. Dynamical lattice simulations of DK and [Formula: see text] scattering and the extraction of their phase shifts may help resolve the underlying structure of Dsj(2317), Dsj(2460) and X(3872).
FISSION FRAGMENT ANGULAR DISTRIBUTION IN 24Mg INDUCED REACTIONS ON 192Os AND 197Au
Authors: TRIPATHI R. , SUDARSHAN K. , SODAYE S. , GOSWAMI A. , REDDY A. V. R. , MAHATA K.
Published: February 2008

Angular distributions of fission fragments have been measured in 24 Mg + 192 Os and 24 Mg + 197 Au reactions at E lab = 128 MeV which is close to entrance channel Coulomb barrier. Experimental angular anisotropies were in reasonably good agreement with those calculated using the statistical theory. Analysis of the angular distribution data of the present study and of our earlier measurement in 19 F + 197 Au reaction has shown that contribution from non-compound nucleus fission in these systems is not significant.
CALCULATION OF FISSION FRAGMENT ANGULAR ANISOTROPY IN HEAVY-ION INDUCED FISSION
Authors: SOHEYLI S. , NOSHAD H. , ZIAIAN I.
Published: February 2008

Fission fragment angular anisotropies from 16 O + 232 Th , 12 C + 236 U , 11 B + 237 Np , 14 N + 232 Th , 11 B + 235 U and 12 C + 232 Th systems were calculated by means of the standard saddle point statistical model (SSPSM). The results were obtained with and without neutron emission correction in the reactions, and comparisons were made with the corresponding experimental data. The normal and anomalous behaviors of fission fragment anisotropies are extensively discussed.
COMPLETE AND INCOMPLETE FUSION REACTIONS OF 16O WITH 75As AT INCIDENT ENERGIES BELOW 7 MeV/A
Authors: GUIN R. , SAHA S. K.
Published: February 2008

Excitation functions and differential recoil range distributions in the interaction of 16 O with 75 As have been measured to investigate complete and incomplete fusion reactions. The measured cross sections were compared with theoretical calculations using the computer code ALICE-91. The results indicated predominant incomplete fusion processes in the production of near target products. This was further confirmed by recoil range distribution studies of the products at 104 MeV of beam energy. The relative contributions of complete and incomplete fusion channels are estimated from recoil range distribution measurements.
Genetically Engineered Plants and Foods: A Scientist's Analysis of the Issues (Part I)
Authors: Lemaux Peggy G.
Published: February 2008

Through the use of the new tools of genetic engineering, genes can be introduced into the same plant or animal species or into plants or animals that are not sexually compatible—the latter is a distinction with classical breeding. This technology has led to the commercial production of genetically engineered (GE) crops on approximately 250 million acres worldwide. These crops generally are herbicide and pest tolerant, but other GE crops in the pipeline focus on other traits. For some farmers and consumers, planting and eating foods from these crops are acceptable; for others they raise issues related to safety of the foods and the environment. In Part I of this review some general and food issues raised regarding GE crops and foods will be addressed. Responses to these issues, where possible, cite peer-reviewed scientific literature. In Part II to appear in 2009, issues related to environmental and socioeconomic aspects of GE crops and foods will be covered.
Contemporary Trends in the Pharmacological and Extracorporeal Management of Heart Failure
Authors: Kazory Amir , Ross Edward A.
Published: February 2008

Heart failure and chronic kidney disease share a number of risk factors and pathophysiological pathways. These 2 pathological processes coexist in large numbers of patients. Whereas the presence of chronic kidney disease in patients with heart failure adversely influences their survival, cardiovascular disease is the major cause of mortality in individuals with chronic kidney disease. The management of heart failure by cardiologists has recently expanded from pharmacological treatment to extracorporeal strategies; the interaction between (and concurrent use of) these approaches traditionally has been part of nephrology care and training. The purpose of this review is to explore these management strategies from a nephrologic standpoint and cover the pathophysiology of diuretic resistance, new pharmaceutical strategies to induce natriuresis or aquaresis, and the physiological basis and theoretical advantages of fluid removal by nontraditional peritoneal or hemofiltration approaches. This review also focuses on the technical features, safety, and potential risks of dedicated ultrafiltration devices that do not require dialysis staff or facilities and that are now readily available to nonnephrologists.
When Loading Working Memory Reduces Distraction: Behavioral and Electrophysiological Evidence from an Auditory-Visual Distraction Paradigm
Authors: SanMiguel Iria , Corral María-José , Escera Carles
Published: February 2008

The sensitivity of involuntary attention to top-down modulation was tested using an auditory-visual distraction task and a working memory (WM) load manipulation in subjects performing a simple visual classification task while ignoring contingent auditory stimulation. The sounds were repetitive standard tones (80%) and environmental novel sounds (20%). Distraction caused by the novel sounds was compared across a 1-back WM condition and a no-memory control condition, both involving the comparison of two digits. Event-related brain potentials (ERPs) to the sounds were recorded, and the N1/MMN (mismatch negativity), novelty-P3, and RON components were identified in the novel minus standard difference waveforms. Distraction was reduced in the WM condition, both behaviorally and as indexed by an attenuation of the late phase of the novelty-P3. The transient/change detection mechanism indexed by MMN was not affected by the WM manipulation. Sustained, slow frontal and parietal waveforms related to WM processes were found on the standard ERPs. The present results indicate that distraction caused by irrelevant novel sounds is reduced when a WM component is involved in the task, and that this modulation by WM load takes place at a late stage of the orienting response, all in all confirming that involuntary attention is under the control of top-down mechanisms. Moreover, as these results contradict predictions of the load theory of selective attention and cognitive control, it is suggested that the WM load effects on distraction depend on the nature of the distractor-target relationships.
Effects of Stimulus Difficulty and Repetition on Printed Word Identification: An fMRI Comparison of Nonimpaired and Reading-disabled Adolescent Cohorts
Authors: Pugh Kenneth R. , Frost Stephen J. , Sandak Rebecca , Landi Nicole , Rueckl Jay G. , Constable R. Todd , Seidenberg Mark S. , Fulbright Robert K. , Katz Leonard , Mencl W. Einar
Published: February 2008

Functional neuroimaging studies indicate that a primary marker of specific reading disability (RD) is reduced activation of left hemisphere (LH) posterior regions during performance of reading tasks. However, the severity of this disruption, and the extent to which these LH systems might be available for reading under any circumstances, is unclear at present. Experiment 1 examined the cortical effects of stimulus manipulations (frequency, imageability, consistency) that have known facilitative effects on reading performance for both nonimpaired (NI) and RD readers. Experiment 2 examined stimulus repetition, another facilitative variable, in an additional sample of adolescent NI and RD readers. For NI readers, factors that made words easier to process were associated with relatively reduced activation. For RD readers, facilitative factors resulted in increased activation in these same reading-related sites, suggesting that the LH reading circuitry in adolescent RD is poorly trained but not wholly disrupted.
Left Posterior Temporal Regions are Sensitive to Auditory Categorization
Authors: Desai Rutvik , Liebenthal Einat , Waldron Eric , Binder Jeffrey R.
Published: February 2008

Recent studies suggest that the left superior temporal gyrus and sulcus (LSTG/S) play a role in speech perception, although the precise function of these areas remains unclear. Here, we test the hypothesis that regions in the LSTG/S play a role in the categorization of speech phonemes, irrespective of the acoustic properties of the sounds and prior experience of the listener with them. We examined changes in functional magnetic resonance imaging brain activation related to a perceptual shift from nonphonetic to phonetic analysis of sine-wave speech analogs. Subjects performed an identification task before scanning and a discrimination task during scanning with phonetic (P) and nonphonetic (N) sine-wave sounds, both before (Pre) and after (Post) being exposed to the phonetic properties of the P sounds. Behaviorally, experience with the P sounds induced categorical identification of these sounds. In the PostP > PreP and PostP > PostN contrasts, an area in the posterior LSTG/S was activated. For both P and N sounds, the activation in this region was correlated with the degree of categorical identification in individual subjects. The results suggest that these areas in the posterior LSTG/S are sensitive neither to the acoustic properties of speech nor merely to the presence of phonetic information, but rather to the listener's awareness of category representations for auditory inputs.
Class Information Predicts Activation by Object Fragments in Human Object Areas
Authors: Lerner Yulia , Epshtein Boris , Ullman Shimon , Malach Rafael
Published: February 2008

Object-related areas in the ventral visual system in humans are known from imaging studies to be preferentially activated by object images compared with noise or texture patterns. It is unknown, however, which features of the object images are extracted and represented in these areas. Here we tested the extent to which the representation of visual classes used object fragments selected by maximizing the information delivered about the class. We tested functional magnetic resonance imaging blood oxygenation level-dependent activation of highly informative object features in low- and high-level visual areas, compared with noninformative object features matched for low-level image properties. Activation in V1 was similar, but in the lateral occipital area and in the posterior fusiform gyrus, activation by “informative” fragments was significantly higher for three object classes. Behavioral studies also revealed high correlation between performance and fragments information. The results show that an objective class-information measure can predict classification performance and activation in human object-related areas.
Speeding Up Syntax: On the Relative Timing and Automaticity of Local Phrase Structure and Morphosyntactic Processing as Reflected in Event-related Brain Potentials
Authors: Hasting Anna S. , Kotz Sonja A.
Published: February 2008

Neurolinguistic research utilizing event-related brain potentials (ERPs) typically relates syntactic phrase structure processing to an early automatic processing stage around 150 to 200 msec, whereas morphosyntactic processing is associated with a later and somewhat more attention-dependent processing stage between 300 and 500 msec. However, recent studies have challenged this position by reporting highly automatic ERP effects for morphosyntax in the 100 to 200 msec time range. The present study aimed at determining the factors that could contribute to such shifts in latency and automaticity. In two experiments varying the degree of attention, German phrase structure and morphosyntactic violations were compared in conditions in which the locality of the violated syntactic relation, as well as the violation point and the acoustic properties of the speech stimuli, were strictly controlled for. A negativity between 100 and 300 msec after the violation point occurred in response to both types of syntactic violations and independently of the allocation of attentional resources. These findings suggest that the timing and automaticity of ERP effects reflecting specific syntactic subprocesses are influenced to a larger degree by methodological than by linguistic factors, and thus, need to be regarded as relative rather than fixed to temporally successive processing stages.
Hand and Mouth: Cortical Correlates of Lexical Processing in British Sign Language and Speechreading English
Authors: Capek Cheryl M. , Waters Dafydd , Woll Bencie , MacSweeney Mairéad , Brammer Michael J. , McGuire Philip K. , David Anthony S. , Campbell Ruth
Published: February 2008

Spoken languages use one set of articulators—the vocal tract, whereas signed languages use multiple articulators, including both manual and facial actions. How sensitive are the cortical circuits for language processing to the particular articulators that are observed? This question can only be addressed with participants who use both speech and a signed language. In this study, we used functional magnetic resonance imaging to compare the processing of speechreading and sign processing in deaf native signers of British Sign Language (BSL) who were also proficient speechreaders. The following questions were addressed: To what extent do these different language types rely on a common brain network? To what extent do the patterns of activation differ? How are these networks affected by the articulators that languages use? Common peri-sylvian regions were activated both for speechreading English words and for BSL signs. Distinctive activation was also observed reflecting the language form. Speechreading elicited greater activation in the left mid-superior temporal cortex than BSL, whereas BSL processing generated greater activation at the temporo-parieto-occipital junction in both hemispheres. We probed this distinction further within BSL, where manual signs can be accompanied by different types of mouth action. BSL signs with speech-like mouth actions showed greater superior temporal activation, whereas signs made with non-speech-like mouth actions showed more activation in posterior and inferior temporal regions. Distinct regions within the temporal cortex are not only differentially sensitive to perception of the distinctive articulators for speech and for sign but also show sensitivity to the different articulators within the (signed) language.
Seeing and Hearing Meaning: ERP and fMRI Evidence of Word versus Picture Integration into a Sentence Context
Authors: Willems Roel M. , Özyürek Aslı , Hagoort Peter
Published: February 2008

Understanding language always occurs within a situational context and, therefore, often implies combining streams of information from different domains and modalities. One such combination is that of spoken language and visual information, which are perceived together in a variety of ways during everyday communication. Here we investigate whether and how words and pictures differ in terms of their neural correlates when they are integrated into a previously built-up sentence context. This is assessed in two experiments looking at the time course (measuring event-related potentials, ERPs) and the locus (using functional magnetic resonance imaging, fMRI) of this integration process. We manipulated the ease of semantic integration of word and/or picture to a previous sentence context to increase the semantic load of processing. In the ERP study, an increased semantic load led to an N400 effect which was similar for pictures and words in terms of latency and amplitude. In the fMRI study, we found overlapping activations to both picture and word integration in the left inferior frontal cortex. Specific activations for the integration of a word were observed in the left superior temporal cortex. We conclude that despite obvious differences in representational format, semantic information coming from pictures and words is integrated into a sentence context in similar ways in the brain. This study adds to the growing insight that the language system incorporates (semantic) information coming from linguistic and extralinguistic domains with the same neural time course and by recruitment of overlapping brain areas.
Novel Scenes Improve Recollection and Recall of Words
Authors: Fenker Daniela B. , Frey Julietta U. , Schuetze Hartmut , Heipertz Dorothee , Heinze Hans-Jochen , Duzel Emrah
Published: February 2008

Exploring a novel environment can facilitate subsequent hippocampal long-term potentiation in animals. We report a related behavioral enhancement in humans. In two separate experiments, recollection and free recall, both measures of hippocampus-dependent memory formation, were enhanced for words studied after a 5-min exposure to unrelated novel as opposed to familiar images depicting indoor and outdoor scenes. With functional magnetic resonance imaging, the enhancement was predicted by specific activity patterns observed during novelty exposure in parahippocampal and dorsal prefrontal cortices, regions which are known to be linked to attentional orienting to novel stimuli and perceptual processing of scenes. Novelty was also associated with activation of the substantia nigra/ventral tegmental area of the midbrain and the hippocampus, but these activations did not correlate with contextual memory enhancement. These findings indicate remarkable parallels between contextual memory enhancement in humans and existing evidence regarding contextually enhanced hippocampal plasticity in animals. They provide specific behavioral clues to enhancing hippocampus-dependent memory in humans.
Productive Vocabulary Size Predicts Event-related Potential Correlates of Fast Mapping in 20-Month-Olds
Authors: Torkildsen Janne von Koss , Svangstu Janne Mari , Hansen Hanna Friis , Smith Lars , Simonsen Hanne Gram , Moen Inger , Lindgren Magnus
Published: February 2008

Although it is well documented that children undergo a productive vocabulary spurt late in the second year, it is unclear whether this development is accompanied by equally significant advances in receptive word processing. In the present study, we tested an electrophysiological procedure for assessing receptive word learning in young children, and the impact of productive vocabulary size for performance in this task. We found that 20-month-olds with high productive vocabularies displayed an N400 incongruity effect to violations of trained associations between novel words and pictures, whereas 20-month-olds with low productive vocabularies did not. However, both high and low producers showed an N400 effect for common real words paired with an incongruous object. These findings indicate that there may be substantial differences in receptive fast mapping efficiency between typically developing children who have reached a productive vocabulary spurt and typically developing children who have not yet reached this productive spurt.
The Speed of Orthographic Processing during Lexical Decision: Electrophysiological Evidence for Independent Coding of Letter Identity and Letter Position in Visual Word Recognition
Authors: Mariol Marina , Jacques Corentin , Schelstraete Marie-Anne , Rossion Bruno
Published: February 2008

Adults can decide rapidly if a string of letters is a word or not. However, the exact time course of this discrimination is still an open question. Here we sought to track the time course of this discrimination and to determine how orthographic information—letter position and letter identity—is computed during reading. We used a go/no-go lexical decision task while recording event-related potentials (ERPs). Subjects were presented with single words (go trials) and pseudowords (no-go trials), which varied in orthographic conformation, presenting either a double consonant frequently doubled (i.e., “ss”) or never doubled (i.e., “zz”) (identity factor); and a position of the double consonant was which either legal or illegal (position factor), in a 2 × 2 factorial design. Words and pseudowords clearly differed as early as 230 msec. At this latency, ERP waveforms were modulated both by the identity and by the position of letters: The fronto-central no-go N2 was the smallest in amplitude and peaked the earliest to pseudowords presenting both an illegal double-letter position and an identity never encountered. At this stage, the two factors showed additive effects, suggesting an independent coding. The factors of identity and position of double letters interacted much later in the process, at the P3 level, around 300–400 msec on frontal and central sites, in line with the lexical decision data obtained in the behavioral study. Overall, these results show that the speed of lexical decision may depend on orthographic information coded independently by the identity and position of letters in a word.
Endogenous Control and Task Representation: An fMRI Study in Algebraic Problem-solving
Authors: Stocco Andrea , Anderson John R.
Published: February 2008

The roles of prefrontal and anterior cingulate cortices have been widely studied, yet little is known on how they interact to enable complex cognitive abilities. We investigated this issue in a complex yet well-defined symbolic paradigm: algebraic problem solving. In our experimental problems, the demands for retrieving arithmetic facts and maintaining intermediate problem representations were manipulated separately. An analysis of functional brain images acquired while participants were solving the problems confirmed that prefrontal regions were affected by the retrieval of arithmetic facts, but only scarcely by the need to manipulate intermediate forms of the equations, hinting at a specific role in memory retrieval. Hemodynamic activity in the dorsal cingulate, on the contrary, increased monotonically as more information processing steps had to be taken, independent of their nature. This pattern was essentially mimicked in the caudate nucleus, suggesting a related functional role in the control of cognitive actions. We also implemented a computational model within the Adaptive Control of Thought—Rational (ACT-R) cognitive architecture, which was able to reproduce both the behavioral data and the time course of the hemodynamic activity in a number of relevant regions of interest. Therefore, imaging results and computer simulation provide evidence that symbolic cognition can be explained by the functional interaction of medial structures supporting control and serial execution, and prefrontal cortices engaged in the on-line retrieval of specific relevant information.
Processing Pronouns without Antecedents: Evidence from Event-related Brain Potentials
Authors: Filik Ruth , Sanford Anthony J. , Leuthold Hartmut
Published: February 2008

Pronouns that do not have explicit antecedents typically cause processing problems. We investigate a specific example in which this may not be the case, as in “At the interview, they asked really difficult questions,” where the plural pronoun they has no explicit antecedent, yet is intuitively easy to process. Some unspecified but constrained set of individuals (the interview panel or the company) can be inferred as the referent, but it is not crucial to determine specifically which entities are being referred to. We propose that this contrasts with the processing of singular pronouns (he or she), for which it is necessary to determine a specific referent. We used event-related brain potentials to investigate how readers process the pronoun (they vs. he/she) in these cases. Sentences were placed in a context that either did or did not contain an explicit antecedent for the pronoun. There were two key findings. Firstly, when there was no explicit antecedent, a larger fronto-central positivity was observed 750 msec after pronoun onset for he/she than they, possibly reflecting the additional difficulty involved in establishing a referent for he/she than for they when no explicit referent is available. Secondly, there was a larger N400-like deflection evoked by he/she than they, regardless of whether there was an explicit antecedent for the pronoun. We suggest that this is due to the singular pronouns bringing about a greater integration effort than the plural pronoun. This observation adds to a growing body of research revealing fundamental differences in the way these pronouns are handled by the language processor.
The Short and Long of It: Neural Correlates of Temporal-order Memory for Autobiographical Events
Authors: St. Jacques Peggy , Rubin David C. , LaBar Kevin S. , Cabeza Roberto
Published: February 2008

Previous functional neuroimaging studies of temporal-order memory have investigated memory for laboratory stimuli that are causally unrelated and poor in sensory detail. In contrast, the present functional magnetic resonance imaging (fMRI) study investigated temporal-order memory for autobiographical events that were causally interconnected and rich in sensory detail. Participants took photographs at many campus locations over a period of several hours, and the following day they were scanned while making temporal-order judgments to pairs of photographs from different locations. By manipulating the temporal lag between the two locations in each trial, we compared the neural correlates associated with reconstruction processes, which we hypothesized depended on recollection and contribute mainly to short lags, and distance processes, which we hypothesized to depend on familiarity and contribute mainly to longer lags. Consistent with our hypotheses, parametric fMRI analyses linked shorter lags to activations in regions previously associated with recollection (left prefrontal, parahippocampal, precuneus, and visual cortices), and longer lags with regions previously associated with familiarity (right prefrontal cortex). The hemispheric asymmetry in prefrontal cortex activity fits very well with evidence and theories regarding the contributions of the left versus right prefrontal cortex to memory (recollection vs. familiarity processes) and cognition (systematic vs. heuristic processes). In sum, using a novel photo-paradigm, this study provided the first evidence regarding the neural correlates of temporal-order for autobiographical events.
Aerosol–Cloud Interactions in a Mesoscale Model. Part I: Sensitivity to Activation and Collision–Coalescence
Authors: Ivanova Irena T. , Leighton Henry G.
Published: February 2008

High-resolution numerical simulations of the aerosol–cloud feedbacks are performed with a mesoscale model. The multimodal aerosol species, added to the model, and the cloud species were represented by two spectral moments. The aerosol sources include particle activation, solute transfer between drops due to collision and coalescence of drops, and particle regeneration. A summertime case was simulated consisting of a cold frontal cloud system and a postfrontal stratus. Experiments with both simple and mechanistic activation parameterization of aerosol and with one and two aerosol modes were performed. Verification was made of the stratus properties against measurements taken during the Radiation Aerosol and Cloud Experiment (RACE).

The results demonstrate a significant sensitivity of the stratus and of the frontal system to the aerosol and a moderate impact on the particle spectrum of drop collision–coalescence. The stratus simulation with mechanistic activation and unimodal aerosol showed the best agreement of droplet concentration with the observations, and the simulations with mechanistic activation and a bimodal aerosol and with simple activation underestimated the droplet concentration. A similar high sensitivity was found for the frontal precipitation intensity. Drop collision–coalescence in the frontal system was found to have an impact on the particle mean radius whose magnitude amounted to 10% and 15% for one and multiple cloud cycles, respectively. This impact was also found to be highly variable in space. The modified particle spectrum, following activation in clouds, was found to increase droplet concentration.
Aerosol–Cloud Interactions in a Mesoscale Model. Part II: Sensitivity to Aqueous-Phase Chemistry
Authors: Ivanova Irena T. , Leighton Henry G.
Published: February 2008

The feedbacks between aerosols, cloud microphysics, and cloud chemistry are investigated in a mesoscale model. A simple bulk aqueous-phase sulfur chemistry scheme was fully coupled to the existing aerosol and microphysics schemes. The representation of aerosol and microphysics follows the explicit bulk double-moment approach. A case of summertime stratocumulus cloud system is simulated at high resolution (3-km grid spacing), and the evolution of an observed continental aerosol spectrum that changes during the course of the simulation as a result of cloud processing is examined.

The results demonstrate that the bulk approach to the aerosol and droplet spectra correctly represents the feedbacks in the coupled system. The simulations capture the characteristic bimodal aerosol size spectrum resulting from cloud processing, with the first mode consisting of particles that did not participate as cloud condensation nuclei and the second mode, in the region of 0.08–0.12-μm radii, comprising the particles that were affected by processing. New information is revealed about the impact of the two main processing pathways and about the spatial distribution of the processed aerosol. One cycle of physical processing produced a relatively modest impact of 3%–5% on the processed particle mean radius of the order that was comparable to the impact of chemical processing, while continuous physical recycling produced a much larger impact as high as 30%–50%. A strong constraint on the chemical processing was found to be the initial chemistry input and the assumption of bulk chemical composition. Simple tests with a more slowly depleting primary oxidant (H2O2) and including the droplet chemical heterogeneity effect favor stronger sulfate production, by, respectively, the H2O2 and O3 oxidation reaction, and both show a larger impact on the processed particle mean radius of similar magnitude, 10%–20%. Spatially, the impact of processing is found initially in the downdraft regions below cloud and at later times at substantial distances downwind. It is shown that cloud processing can either enhance or suppress the number of activated drops in subsequent cycles.
Weather-Layer Dynamics of Baroclinic Eddies and Multiple Jets in an Idealized General Circulation Model
Authors: O’Gorman Paul A. , Schneider Tapio
Published: February 2008

The general circulation and the behavior of multiple jets and baroclinic eddies are described for an atmosphere in which meridional potential temperature gradients and eddies are confined to a weather layer. The weather layer is separated from the frictional lower boundary by a statically stable barotropic layer with significant mass. Closure of the zonal momentum budget in the resulting circulation is achieved through ageostrophic meridional cells that extend to the lower boundary, at which momentum is dissipated. In a series of simulations with a multilevel primitive equation model, dynamic changes in the static stability of the weather layer are found to be critical in determining the scaling of the baroclinic eddies, an effect not captured in quasigeostrophic models. For simulations with a single jet in each hemisphere, the static stability of the weather layer adjusts so that a significant inverse energy cascade to scales larger than the Rossby deformation radius does not occur. The eddy length is found to scale with both the Rossby deformation radius and the Rhines scale. Simulations with larger planetary radii and low pole-to-equator temperature gradients exhibit multiple jets in each hemisphere. Eddy lengths and energies for the jet nearest the equator in each hemisphere have the same scaling as those in the single-jet simulations. Similar scalings are found for jets farther poleward but with different constants of proportionality that are consistent with more supercritical eddies. The local eddy length is found to have only a weak variation with latitude, and the local meridional jet spacing is found to scale with the local eddy length in all cases. Insights from the weather-layer simulations may be relevant to circulations in gas giant planets and the ocean.
A Comparison of Statistical Dynamical and Ensemble Prediction Methods during Blocking
Authors: O’Kane Terence J. , Frederiksen Jorgen S.
Published: February 2008

In this paper error growth is examined using a family of inhomogeneous statistical closure models based on the quasi-diagonal direct interaction approximation (QDIA), and the results are compared with those based on ensembles of direct numerical simulations using bred perturbations. The closure model herein includes contributions from non-Gaussian terms, is realizable, and conserves kinetic energy and enstrophy. Further, unlike previous approximations, such as those based on cumulant-discard (CD) and quasi-normal (QN) hypotheses (Epstein and Fleming), the QDIA closure is stable for long integration times and is valid for both strongly non-Gaussian and strongly inhomogeneous flows. The performance of a number of variants of the closure model, incorporating different approximations to the higher-order cumulants, is examined. The roles of non-Gaussian initial perturbations and small-scale noise in determining error growth are examined. The importance of the cumulative contribution of non-Gaussian terms to the evolved error tendency is demonstrated, as well as the role of the off-diagonal covariances in the growth of errors. Cumulative and instantaneous errors are quantified using kinetic energy spectra and a small-scale palinstrophy production measure, respectively. As a severe test of the methodology herein, synoptic situations during a rapid regime transition associated with the formation of a block over the Gulf of Alaska are considered. In general, the full QDIA closure results compare well with the statistics of direct numerical simulations.
A Study of Two-Dimensional Dry Convective Plume Modes with Variable Critical Level Height
Authors: Kiefer Michael T. , Lin Yuh-Lang , Charney Joseph J.
Published: February 2008

This study investigates the impact of wind speed and critical level height on dry convection above a prescribed heat source. This is done using the Advanced Regional Prediction System (ARPS) model in its two-dimensional form with an imposed 400-K soil potential temperature perturbation. The result of these experiments is the identification of three modes of convective plumes. The first, termed multicell convective plumes, is analogous to multicell convection generated from squall-line cold pools in the moist atmosphere. The second mode, a deep wave mode, consists of disturbances with wavelengths of 7–10 km and results from the multicell plumes perturbing the dynamically unstable shear flow centered at the critical level. The third mode, termed the intense fire plume, has stronger updrafts than the multicell mode and is marked by quasi-stationary movement and substantial low-level inflow and upper-level outflow. The presence of a critical level is shown to be crucial to the development of both the deep wave and intense plume modes. The intense fire plume mode is most consistent with the so-called fire storm, or conflagration phenomenon, in which strong updrafts and low-level indrafts can produce mesocyclones and tornadic fire whirls capable of significant damage. This study marks an important step in understanding the dynamics behind the fire storm phenomenon, as well as other types of convection (multicell and deep wave) that may be generated by a fire.
Two-Dimensional Idealized Simulations of the Impact of Multiple Windward Ridges on Orographic Precipitation
Authors: Colle Brian A.
Published: February 2008

This paper presents two-dimensional (2D) idealized simulations at 1-km grid spacing using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) in order to illustrate how a series of ridges along a broad windward slope can impact the precipitation distribution and simulated microphysics. The number of windward ridges for a 2000-m mountain of 50-km half-width is varied from 0 to 16 over a 150-km distance using different stratifications, freezing levels, uniform ambient flows, and ridge amplitudes.

A few (200–400 m) windward ridges can enhance the precipitation locally over each ridge crest by a factor of 2–3. Meanwhile, a series of 8–16 ridges that are 200–400 m in height can increase the net precipitation averaged over the windward slope by 10%–35%. This average precipitation enhancement is maximized when the ridge spacing is relatively small (<20 km), since there is less time for subsidence drying within the valleys and the mountain waves become more evanescent, which favors a simple upward and downward motion couplet over each ridge. In addition, small ridge spacing is shown to have a synergistic effect on precipitation over the lower windward slope, in which an upstream ridge helps increase the precipitation over the adjacent downwind ridge. There is little net precipitation enhancement by the ridges for small moist Froude numbers (Fr < 0.8), since flow blocking limits the flow up and over each ridge. For a series of narrow ridges (∼10 km wide), the largest precipitation enhancement for a 500-mb freezing level occurs over lower windward slope of the barrier through warm-rain processes. In contrast, a 1000-mb freezing level has the largest precipitation enhancement over the middle and upper portions of a barrier for a series of narrow (∼10 km wide) ridges given the horizontal advection of snow aloft.