bluuebunny/crossref_metadata_2025 huggingface dataset:
Jellyfish blooms:Crambionella orsini(Scyphozoa: Rhizostomeae) in the Gulf of Oman, Iran, 2002–2003
Authors: Daryanabard Reza , Dawson Michael N.
Published: May 2008

In 2002, a jellyfish bloom occurred throughout the Gulf of Oman and the Persian Gulf causing decreased catch in artisanal and industrial fisheries, damage to fishing gear, interrupted operation of desalination plants, and damage to the seawater cooling systems of coastal power plants. The cause and source of the bloom and the species of medusa were unknown. Here, the temporal and spatial distribution of the medusa are described using data from incidental catches in Iranian fisheries surveys, and morphological and molecular evidence are used to identify the medusa asCrambionella orsini(Vanhöffen). This species is endemic to the western Indian Ocean and adjacent basins which dismisses species introduction as the cause of this bloom. Furthermore, because the bloom was geographically widespread, it probably was not caused by local coastal degradation. Although human activities with large-scale effects cannot be ruled out, large-scale oceanographic or ecosystem conditions, perhaps part of natural climate cycles, that yielded moderate sea surface temperatures (in terms of the annual mean monthly anomaly for each year since 1982) were the most likely causes of the bloom of this endemic jellyfish.
Radula synthesis by three species of iron mineralizing molluscs: production rate and elemental demand
Authors: Shaw J.A. , Macey D.J. , Brooker L.R.
Published: May 2008

A cold-shock technique was used to determine radula production rates for the chitonsAcanthopleura hirtosaandPlaxiphora albida, and for the limpetPatelloida alticostata, which replaced their radular teeth at rates of 0.40, 0.36 and 0.51 rows d−1, respectively. These rates are far slower than those determined previously for non-iron-mineralizing molluscs, suggesting that the improved working life of the teeth afforded by iron-mineralization acts to significantly reduce replacement rates. In addition, inductively coupled plasma-atomic emission spectroscopy has been used to determine the quantity of iron and other elements comprising the radula of each species. These data, used in conjunction with the radula production rates, reveal thatA. hirtosa,Plaxiphora albidaandPatelloida alticostatahave daily radula mineralization requirements for iron of 3.06, 4.12 and 0.55 μg, respectively. Such information is vital for continuing studies related to the cellular delivery of ions and subsequent biomineralization of the tooth cusps in chitons and limpets.
The phylogenetic relationships between Amphinomidae, Archinomidae and Euphrosinidae (Amphinomida: Aciculata: Polychaeta), inferred from molecular data
Authors: Wiklund Helena , Nygren Arne , Pleijel Fredrik , Sundberg Per
Published: May 2008

Amphinomida is an ‘isolated’ clade within the polychaete group Aciculata and traditionally includes the families Amphinomidae, Archinomidae and Euphrosinidae. Archinomidae were erected for a single species, the hydrothermal vent polychaeteArchinome rosacea.Originally,A. rosaceawas assigned to Euphrosinidae although it shares more morphological similarities with Amphinomidae. In this study we assess the position of Archinome, Euphrosinidae and Amphinomidae by using molecular data from nuclear 18S rDNA and 28S rDNA. Parsimony, maximum likelihood and Bayesian analyses are performed on the nucleotide datasets covering in total 19 terminals from Amphinomidae, Euphrosinidae, Archinomidae and outgroups. Our results conclusively show that Euphrosinidae and Amphinomidae are sister taxa and that Archinome is sister to Chloeia within Amphinomidae. Based on these results the family name Archinomidae is treated as a junior synonym of Amphinomidae.
Epibiont species richness varies between holdfasts of a northern and a southerly distributed kelp species
Authors: Blight A.J. , Thompson R.C.
Published: May 2008

All habitats are modified to some extent by the species that live within them. Kelp is known to have a very strong influence on the surrounding environment providing a habitat for a wide range of organisms including marine mammals, fish and invertebrates. Here we examine the consequences of a subtle shift in the relative abundance of two species of kelp, Laminaria digitata and Laminaria ochroleuca, and compare the holdfast epibiont assemblages on both. These species are morphologically very similar and both provide important biologically generated habitats. The distribution of these kelp species is predicted to alter as a consequence of climate change with L. ochroleuca extending its range northward and potentially outcompeting L. digitata in the north-eastern Atlantic. The epibiont fauna common to both species of kelp were predominantly made up of annelids, molluscs and bryozoans. Most of the epibiont flora we found on the holdfasts was from the class Rhodophyceae. Multivariate analysis showed that the richness of epibiont species associated with L. ochroleuca was significantly lower, a mean of 0.62 species per cm3, when compared to the northern species, L. digitata which had a mean of 1.13 species per cm3. Laminaria digitata also had more unique epibiont species indicating that species richness of holdfast assemblages is likely to decline if L. digitata is replaced by L. ochroleuca. These data illustrate the importance of studying biologically generated habitats when considering the potential consequences of climate change on marine assemblages.
The reinterpretation hypothesis: Explanation or redescription?
Authors: Bermúdez José Luis
Published: May 2008

Penn et al. propose the relational reinterpretation hypothesis as an explanation of the profound discontinuities that they identify between human and nonhuman cognition. This hypothesis is not a genuine replacement for the explanations that they reject, however, because as it stands, it simply redescribes the phenomena it is trying to explain.
Darwin's last word: How words changed cognition
Authors: Bickerton Derek
Published: May 2008

Although Penn et al. make a good case for the existence of deep cognitive discontinuity between humans and animals, they fail to explain how such a discontinuity could have evolved. It is proposed that until the advent of words, no species had mental representations over which higher-order relations could be computed.
Bottlenose dolphins understand relationships between concepts
Authors: Herman Louis M. , Uyeyama Robert K. , Pack Adam A.
Published: May 2008

We dispute Penn et al.'s claim of the sharp functional discontinuity between humans and nonhumans with evidence in bottlenose dolphins(Tursiops truncatus)of higher-order generalizations: spontaneous integration of previously learned rules and concepts in response to novel stimuli. We propose that species-general explanations that are “bottom-up” in approach are more plausible than Penn et al.'s innatist approach of a genetically prespecified supermodule.
Quotidian cognition and the human-nonhuman “divide”: Just more or less of a good thing?
Authors: Rendall Drew , Vokey John R. , Notman Hugh
Published: May 2008

We make three points: (1) Overlooked studies of nonhuman communication originally inspired, but no longer support, the blinkered view of mental continuity that Penn et al. critique. (2) Communicative discontinuities between animals and humans might be rooted in social-cognitive discontinuities, reflecting a common lacuna in Penn et al.'s relational reinterpretation mechanism. (3) However, relational reinterpretation need not be a qualitatively new representational process.
If we could talk to the animals
Authors: Siegal Michael , Varley Rosemary
Published: May 2008

The thesis of discontinuity between humans and nonhumans requires evidence from formal reasoning tasks that rules out solutions based on associative strategies. However, insightful problem solving can be often credited through talking to humans, but not to nonhumans. We note the paradox of assuming that reasoning is orthogonal to language and enculturation while employing the criterion of using language to compare what humans and nonhumans know.
Minding the gap: Why there is still no theory in comparative psychology
Authors: Wynne Clive D. L. , Bolhuis Johan J.
Published: May 2008

The prevailing view that there is significant cognitive continuity between humans and other animals is a result of misinterpretations of the role of evolution, combined with anthropomorphism. This combination has often resulted in an over-interpretation of data from animal experiments. Comparative psychology should do what the name indicates: study the cognitive capacities of different species empirically, without naive evolutionary presuppositions.
Visual prediction: Psychophysics and neurophysiology of compensation for time delays
Authors: Nijhawan Romi
Published: May 2008

A necessary consequence of the nature of neural transmission systems is that as change in the physical state of a time-varying event takes place, delays produce error between the instantaneous registered state and the external state. Another source of delay is the transmission of internal motor commands to muscles and the inertia of the musculoskeletal system. How does the central nervous system compensate for these pervasive delays? Although it has been argued that delay compensation occurs late in the motor planning stages, even the earliest visual processes, such as phototransduction, contribute significantly to delays. I argue that compensation is not an exclusive property of the motor system, but rather, is a pervasive feature of the central nervous system (CNS) organization. Although the motor planning system may contain a highly flexible compensation mechanism, accounting not just for delays but also variability in delays (e.g., those resulting from variations in luminance contrast, internal body temperature, muscle fatigue, etc.), visual mechanisms also contribute to compensation. Previous suggestions of this notion of “visual prediction” led to a lively debate producing re-examination of previous arguments, new analyses, and review of the experiments presented here. Understanding visual prediction will inform our theories of sensory processes and visual perception, and will impact our notion of visual awareness.
Anticipation requires adaptation
Authors: Balkenius Christian , Gärdenfors Peter
Published: May 2008

To successfully interact with a dynamic world, our actions must be guided by a continuously changing anticipated future. Such anticipations must be tuned to the processing delays in the nervous system as well as to the slowness of the body, something that requires constant adaptation of the predictive mechanisms, which in turn require that sensory information be processed at different time-scales.
The trade-off between speed and complexity
Authors: Changizi Mark Andrew
Published: May 2008

The hypothesis that there has been selection pressure for mechanisms which enable us to perceive the present tends to be conflated with the hypothesis that there has been selection pressure for mechanisms that compensate for inevitable neural delay. The relationship between the two is more subtle, because increases in neural delay can be advantageous for building more useful perceptions.
Visual prediction as indicated by perceptual adaptation to temporal delays and discrete stimulation
Authors: Cunningham Douglas W.
Published: May 2008

Analogous to prism adaptation, sensorimotor compensation for existing neural delays has been clearly demonstrated. This system can also adapt to new delays, both internal and external. This seems to occur at least partially in the sensor systems, and works for discrete, stationary events. This provides additional evidence for visual prediction, but not in a manner that is consistent with spatial extrapolation.
Asynchronous neural integration: Compensation or computational tolerance and skill acquisition?
Authors: Cutting James E.
Published: May 2008

Nijhawan argues that neural compensation is necessary to account for couplings of perception and action. Although perhaps true in some cases, computational tolerance for asynchronously arriving continuous information is of more importance. Moreover, some of the everyday venues Nijhawan uses to argue for the relevance of prediction and compensation can be better ascribed to skill.
Mental and sensorimotor extrapolation fare better than motion extrapolation in the offset condition
Authors: Kerzel Dirk , Müsseler Jochen
Published: May 2008

Evidence for motion extrapolation at motion offset is scarce. In contrast, there is abundant evidence that subjects mentally extrapolate the future trajectory of weak motion signals at motion offset. Further, pointing movements overshoot at motion offset. We believe that mental and sensorimotor extrapolation is sufficient to solve the problem of perceptual latencies. Both present the advantage of being much more flexible than motion extrapolation.
Unconscious inference and conscious representation: Why primary visual cortex (V1) is directly involved in visual awareness
Authors: Lin Zhicheng
Published: May 2008

The extent to which visual processing can proceed in the visual hierarchy without awareness determines the magnitude of perceptual delay. Increasing data demonstrate that primary visual cortex (V1) is involved in consciousness, constraining the magnitude of visual delay. This makes it possible that visual delay is actually within the optimal lengths to allow sufficient computation; thus it might be unnecessary to compensate for visual delay.

The time delay problem – that perception lives slightly in the past as a result of neural conduction – has recently attracted a considerate amount of attention in the context of the flash-lag effect. The effect refers to a visual illusion wherein a brief flash of light and a continuously moving object that physically align in space and time are perceived to be displaced from one another – the flashed stimulus appears to lag behind the moving object (Krekelberg & Lappe 2001). In the target article, Nijhawan compellingly argues that delay compensation could be undertaken by a predictive process in the feedforward pathways in the vision system. Before jumping into the quest for the mechanism of delay compensation, however, I would like to argue that the magnitude of delay has been overestimated, and that it might even be unnecessary to compensate for such a delay.
Anticipating synchronization as an alternative to the internal model
Authors: Stepp Nigel , Turvey Michael T.
Published: May 2008

The fundamental assumption of compensation for visual delays states that, since delays are dealt with, there must be compensatory mechanisms. These mechanisms are taken to be internal models. Alternatives for delay compensation exist, suggesting that this assumption may not be fundamental, and nor should the existence of internal models be assumed. Delays may even be employed in their own compensation.
Motion as a reference for positions
Authors: van de Grind Wim
Published: May 2008

Is the position of a moving target “predicted”? I argue that we should regard moving targets as the natural (veridical) position references. Motion is probably perceptually absolute, whereas position and time are relative quantities, as in physics. According to this view, processing delays are incorporated in the abstract local signs of motion signals. The flash-lag effect is one case in point.
Compensation for time delays is better achieved in time than in space
Authors: Zago Myrka , Lacquaniti Francesco
Published: May 2008

Mechanisms of visual prediction based on spatial extrapolation work only for targets moving at constant speed, but do not easily accommodate accelerating or decelerating motion. We argue that mechanisms based on temporal extrapolation deal with both uniform and non-uniform motion. We provide behavioural examples from interception of falling objects and suggest possible neurophysiological substrates of time extrapolation.
The Bosnia Genocide Case
Authors: AMERASINGHE C. F.
Published: May 2008

The Bosnia Genocide case dealt with several important matters of international law, apart from the issue of responsibility proper for genocide. The Court began by addressing issues of state succession in order to identify the proper respondent. It then found that the objection to jurisdiction raised by the respondent was res judicata. It held that the Genocide Convention created state responsibility in addition to international criminal responsibility of the individual. The contribution of the judgment to the law of evidence, in particular with reference to the standard and methods of proof, is significant. Finally, the Court applied the codification by the International Law Commission of attribution in state responsibility to the situation before it in deciding that the genocidal acts subject of the case were not attributable to Serbia, while also holding that Serbia was, nevertheless, responsible for omitting to prevent genocide.
State Co-operation and International Criminal Court Bargaining Influence in the Arrest and the Surrender of Suspects
Authors: ROPER STEVEN D. , BARRIA LILIAN A.
Published: May 2008

While much has been written about the formation of the International Criminal Court (ICC), less attention has been focused on the enforcement capability of the Court. As demonstrated by the history of the ad hoc international tribunals, one of the most pressing problems for international criminal courts is the arrest and the surrender of suspects, which often requires substantial bargaining between the court and the state in which the suspect resides. We develop a classification of the issues which have the greatest impact on the bargaining influence of the ICC to secure the arrest of indictees, and apply this classification scheme to a study of the four ongoing situations at the ICC in order to explore the bargaining environment in which the ICC operates. While many of the cases have features which should assist the ICC in bargaining with the state, the situation in Sudan represents the greatest challenge for the Court.
Bargaining for Arrests at the International Criminal Court: A Response to Roper and Barria
Authors: BURKE-WHITE WILLIAM W.
Published: May 2008

This comment questions some of the key assumptions in the article by Roper and Barria with respect to the ICC's power to bargain with territorial states to attain the apprehension and surrender of indictees. The comment notes that, while factors such as the nature of the referral to the Court, the crimes charged, and whether the conflict is still ongoing are likely relevant to the ICC's bargaining power, the effect of these factors is indeterminate. The comment highlights the regional political dimension of the ICC's bargaining leverage in the Great Lakes region of Africa and suggests that the Court's bargaining power is engaged in a path-dependent three-level bargaining game.
The Special Tribunal for Lebanon: Introductory Note
Authors: D'ASPREMONT JEAN , VERMEER-KÜNZLI ANNEMARIEKE
Published: May 2008

On 30 May 2007 the UN Security Council adopted Resolution 1757(2007), creating the Special Tribunal for Lebanon (STL) to try those responsible for the assassination of the former Lebanese prime minister, Rafik Hariri, which also claimed the life of twenty-two other persons. Following sensitive and unsuccessful discussions about the location of the seat of the tribunal, the government of the Netherlands informed the UN Secretary-General in September 2007 that it was favourably disposed to hosting the tribunal and, after three months of negotiations, signed, on 21 December 2007, in accordance with paragraph 1(b) of the resolution, a Headquarters Agreement enabling the seat of the STL to be in the Netherlands.
Three‐dimensional seismic investigations of the Sevastopol mud volcano in correlation to gas/fluid migration pathways and indications for gas hydrate occurrences in the Sorokin Trough (Black Sea)
Authors: Wagner‐Friedrichs M. , Krastel S. , Spiess V. , Ivanov M. , Bohrmann G. , Meisner L.
Published: May 2008

New 3‐D seismic investigations carried out across the Sevastopol mud volcano in the Sorokin Trough present 3‐D seismic data of a mud volcano in the Black Sea for the first time. The studies allow us to image the complex three‐dimensional morphology of a collapse structured mud volcano and to propose an evolution model. The Sevastopol mud volcano is located above a buried diapiric structure with two ridges and controlled by fluid migration along a deep fault system, which developed during the growth of the diapirs in a compressional tectonic system. Overpressured fluids initiated an explosive eruption generating the collapse depression of the Sevastopol mud volcano. Several cones were formed within the depression by subsequent quiet mud extrusions. Although gas hydrates have been recovered at various mud volcanoes in the Sorokin Trough, no gas hydrates were sampled at the Sevastopol mud volcano. A BSR (bottom‐simulating reflector) is missing in the seismic data; however, high‐amplitude reflections (bright spots) observed above the diapiric ridge near the mud volcano at a relatively constant depth correspond to the approximate depth of the base of the gas hydrate stability zone (BGHSZ). Thus we suggest that gas hydrates are present locally where gas/fluid flow occurs related to mud volcanism, i.e., above the diapir and close to the feeder channel of the mud volcano. Depth variations of the bright spots of up to 200 ms TWT might be caused by temperature variations produced by variable fluid flow.
Episodic uplift of the Tianshan Mountains since the late Oligocene constrained by magnetostratigraphy of the Jingou River section, in the southern margin of the Junggar Basin, China
Authors: Ji Junliang , Luo Pan , White Paul , Jiang Hanchao , Gao Ling , Ding Zhongli
Published: May 2008

Thick Cenozoic sediments in the southern margin of the Junggar Basin accumulated in response to the uplift and deformation of the Tianshan Mountains. To better constrain this mountains' tectonic history, we report a detailed magnetostratigraphic study of the Jingou River section, located in the northern piedmont of the Tianshan Mts. A total of 1133 samples were used to establish the magnetostratigraphy of a more than 3000 m thick section from the exposed base of the Anjihaihe Formation to the middle of the Xiyu Formation. Two vertebrate fossil sites and a good correlation with the CK95 geomagnetic polarity timescale suggest that the section was deposited from ∼30.5 to ∼4.6 Ma and the age of the top of the Xiyu formation is ∼2.6 Ma based on an extrapolation of the sedimentation rates. Our results show that significant increases in sedimentation rates as well as notable changes in depositional environments occurred at ∼26–22.5 Ma, ∼13–11 Ma and ∼7 Ma, which represent the initial uplift of the Tianshan Mts. and two subsequent rapid uplift events. In addition, changes in sedimentation rates imply that the uplift of the Tianshan Mts. was episodic, and relatively short, with intervals of intensified deformation with long periods of tectonic weakness or quiescence.
Observations of infragravity waves at the ocean‐bottom broadband seismic stations Endeavour (KEBB) and Explorer (KXBB)
Authors: Dolenc David , Romanowicz Barbara , McGill Paul , Wilcock William
Published: May 2008

We report observations of infragravity waves in the period band 30–400 s at two buried broadband ocean‐bottom seismic stations, KEBB and KXBB, located off the coast of the Pacific Northwest, at a water depth of ∼2370 m. When compared to the energy of short‐period ocean waves recorded at local buoys, the low‐frequency seismic noise is found to be mainly generated when the short‐period ocean waves reach the coast, and not when the storm passes directly above the station. Two types of modulation of the infragravity signal are observed. First, a longer‐period modulation is observed and is best correlated with the energy of the 14–16 s period ocean waves. Second, the entire infragravity band signal is modulated in phase with tides. The results suggest that the infragravity waves originate from the nearshore region east of buoy 46041, which lies off the coast of Washington State, and not from the nearshore regions farther to the north that are closer to KEBB. Strong polarization of the KEBB horizontal motions in the NW–SE direction also suggests that the infragravity waves arrive at KEBB from the SE direction. Since the infragravity waves are not generated uniformly along the shore, modeling of their spatial variability prior to the selection of new sites could help improve the quality of future ocean‐bottom seismic deployments and may also help understand processes at the origin of the Earth's low‐frequency hum.
S-Nitrosation and thiol switching in the mitochondrion: a new paradigm for cardioprotection in ischaemic preconditioning
Authors: Hill Bradford G. , Darley-Usmar Victor M.
Published: May 2008

Understanding the molecular mechanisms through which the heart could be protected from ischaemic injury is of major interest and offers a potential route for the development of new therapies. Recently, several studies have uncovered intriguing relationships between nitric oxide-induced protein thiol modifications and the cardioprotected phenotype. In a highly cited, seminal article published in the Biochemical Journal in 2006, Burwell and colleagues addressed this issue and provided direct evidence for S-nitrosation of complex I of the mitochondrial electron transport chain. These authors were the first to show increased S-nitrosation of mitochondrial proteins from hearts subjected to the cardioprotective process known as ischaemic preconditioning. This study has paved the way for further investigations that collectively reveal a potential link between the mitochondrial S-nitrosoproteome and ischaemic preconditioning.
A molecular view of heterogeneous catalysis
Authors: Christensen Claus Hviid , Nørskov Jens K.
Published: May 2008

The establishment of a molecular view of heterogeneous catalysis has been hampered for a number of reasons. There are, however, recent developments, which show that we are now on the way towards reaching a molecular-scale picture of the way solids work as catalysts. By a combination of new theoretical methods, detailed experiments on model systems, and synthesis and in situ characterization of nano-structured catalysts, we are witnessing the first examples of complete atomic-scale insight into the structure and mechanism of surface-catalyzed reactions. This insight has already proven its value by enabling a rational design of new catalysts. We illustrate this important development in heterogeneous catalysis by highlighting recent examples of catalyst systems for which it has been possible to achieve such a detailed understanding. In particular, we emphasize examples where this progress has made it possible to propose entirely new catalysts, which have then been proven experimentally to exhibit improved performance in terms of catalytic activity or selectivity.
A topos foundation for theories of physics: II. Daseinisation and the liberation of quantum theory
Authors: Döring A. , Isham C. J.
Published: May 2008

This paper is the second in a series whose goal is to develop a fundamentally new way of constructing theories of physics. The motivation comes from a desire to address certain deep issues that arise when contemplating quantum theories of space and time. Our basic contention is that constructing a theory of physics is equivalent to finding a representation in a topos of a certain formal language that is attached to the system. Classical physics arises when the topos is the category of sets. Other types of theory employ a different topos. In this paper, we study in depth the topos representation of the propositional language, PL(S), for the case of quantum theory. In doing so, we make a direct link with, and clarify, the earlier work on applying topos theory to quantum physics. The key step is a process we term “daseinisation” by which a projection operator is mapped to a subobject of the spectral presheaf—the topos quantum analog of a classical state space. In the second part of the paper, we change gear with the introduction of the more sophisticated local language L(S). From this point forward, throughout the rest of the series of papers, our attention will be devoted almost entirely to this language. In the present paper, we use L(S) to study “truth objects” in the topos. These are objects in the topos that play the role of states: a necessary development as the spectral presheaf has no global elements, and hence, there are no micro-states in the sense of classical physics. Truth objects therefore play a crucial role in our formalism.
A topos foundation for theories of physics: III. The representation of physical quantities with arrows δ̆o(A):Σ̱→R≽̱
Authors: Döring A. , Isham C. J.
Published: May 2008

This paper is the third in a series whose goal is to develop a fundamentally new way of viewing theories of physics. Our basic contention is that constructing a theory of physics is equivalent to finding a representation in a topos of a certain formal language that is attached to the system. In Paper II, we studied the topos representations of the propositional language PL(S) for the case of quantum theory, and in the present paper we do the same thing for the, more extensive, local language L(S). One of the main achievements is to find a topos representation for self-adjoint operators. This involves showing that, for any physical quantity A, there is an arrow δ̆o(A):Σ̱→R≽̱, where R≽̱ is the quantity-value object for this theory. The construction of δ̆o(Â) is an extension of the daseinisation of projection operators that was discussed in Paper II. The object R≽̱ is a monoid object only in the topos, τϕ=SetsV(H)op, of the theory, and to enhance the applicability of the formalism, we apply to R≽̱ a topos analog of the Grothendieck extension of a monoid to a group. The resulting object, k(R≽̱), is an abelian group object in τϕ. We also discuss another candidate, R↔̱, for the quantity-value object. In this presheaf, both inner and outer daseinisations are used in a symmetric way. Finally, there is a brief discussion of the role of unitary operators in the quantum topos scheme.
Optimal control design of NMR and dynamic nuclear polarization experiments using monotonically convergent algorithms
Authors: Maximov Ivan I. , Tošner Zdenĕk , Nielsen Niels Chr.
Published: May 2008

Optimal control theory has recently been introduced to nuclear magnetic resonance (NMR) spectroscopy as a means to systematically design and optimize pulse sequences for liquid- and solid-state applications. This has so far primarily involved numerical optimization using gradient-based methods, which allow for the optimization of a large number of pulse sequence parameters in a concerted way to maximize the efficiency of transfer between given spin states or shape the nuclear spin Hamiltonian to a particular form, both within a given period of time. Using such tools, a variety of new pulse sequences with improved performance have been developed, and the NMR spin engineers have been challenged to consider alternative routes for analytical experiment design to meet similar performance. In addition, it has lead to increasing demands to the numerical procedures used in the optimization process in terms of computational speed and fast convergence. With the latter aspect in mind, here we introduce an alternative approach to numerical experiment design based on the Krotov formulation of optimal control theory. For practical reasons, the overall radio frequency power delivered to the sample should be minimized to facilitate experimental implementation and avoid excessive sample heating. The presented algorithm makes explicit use of this requirement and iteratively solves the stationary conditions making sure that the maximum of the objective is reached. It is shown that this method is faster per iteration and takes different paths within a control space than gradient-based methods. In the present work, the Krotov approach is demonstrated by the optimization of NMR and dynamic nuclear polarization experiments for various spin systems and using different constraints with respect to radio frequency and microwave power consumption.
Electronic polarizability and Judd–Ofelt parameters of Nd3+ and Er3+ ions in transparent crystallized glasses with nonlinear optical Ba2TiSi2O8 nanocrystals
Authors: Maruyama N. , Honma T. , Komatsu T.
Published: May 2008

Transparent crystallized glasses consisting of nonlinear optical Ba2TiSi2O8 nanocrystals are prepared in Eu2O3-, Nd2O3-, and Er2O3-doped 40BaO–20TiO2–40SiO2 glasses by a conventional heat treatment method in order to clarify the optical properties of rare-earth (RE) ions in nanocrystals. The electronic polarizabilities of crystallized glasses are evaluated from the values of density and refractive index, and are found to decrease due to nanocrystallization, which indicates that the chemical bonding state in the crystallized glasses is more covalent compared to the precursor glasses. It is proposed from x-ray diffraction analyses and photoluminescence spectra of Eu3+ ions that RE ions such as Nd3+ and Eu3+ are incorporated into Ba2TiSi2O8 nanocrystals. The Judd–Ofelt parameters, Ωt (t=2, 4, and 6), of Nd3+ and Er3+ ions are evaluated from optical absorption spectra. It is observed that the Ω2 parameter of Nd3+ and Er3+ increases largely due to nanocrystallization, suggesting that the site symmetry of Nd3+ and Er3+ ions in nanocrystallized glasses is largely distorted due to their incorporations into the Ba2+ sites in Ba2TiSi2O8 nanocrystals. The change in the Ω4 and Ω6 parameters due to nanocrystallization is small. It is proposed that nonlinear optical Ba2TiSi2O8 nanocrystals including RE ions would have a high potential as active optical materials.
Single particle and pair dynamics in water–formic acid mixtures containing ionic and neutral solutes: Nonideality in dynamical properties
Authors: Gupta Rini , Chandra Amalendu
Published: May 2008

A series of molecular dynamics simulations of water–formic acid mixtures containing either an ionic solute or a neutral hydrophobic solute has been performed to study the extent of nonideality in the dynamics of these solutes for varying composition of the mixtures. The diffusion coefficients of the charged solutes, both cationic and anionic, are found to show nonideal behavior with variation of composition, and similar nonideality is also observed for the diffusion and orientational relaxation of solvent molecules in these mixtures. The diffusion coefficient of a neutral hydrophobic solute, however, decreases monotonically with increase in water concentration. We have also investigated some of the pair dynamical properties such as water-water and water–formic acid hydrogen bond relaxation and residence dynamics of water molecules in water and formic acid hydration shells. The lifetimes of water-water hydrogen bonds are found to be longer than those between formic acid carbonyl oxygen-water hydrogen bonds, whereas the lifetimes of formic acid hydroxyl hydrogen-water hydrogen bonds are longer than those of water-water hydrogen bonds. In general, the hydrogen bond lifetimes for both water-water and water–formic acid hydrogen bonds are found to decrease with increase in water concentration. Residence times of water molecules also show the same trend with increase in formic acid concentration. Interestingly, these pair dynamical properties show a monotonic dependence on composition without any maximum or minimum and behave almost ideally with respect to changes in the composition of the mixtures. The present calculations are performed with fixed-charge nonpolarizable models of the solvent and solute molecules without taking into account many-body polarization effects in an explicit manner.
Interface electronic states and molecular structure of a triarylamine based hole conductor on rutile TiO2(110)
Authors: Johansson E. M. J. , Odelius M. , Karlsson P. G. , Siegbahn H. , Sandell A. , Rensmo H.
Published: May 2008

The molecular and electronic surface structure of a triarylamine based hole-conductor (HC) molecule evaporated onto rutile TiO2(110) single crystal is investigated by means of synchrotron light based photoelectron spectroscopy and x-ray absorption spectroscopy in combination with calculations based on density functional theory. Different amounts of the HC molecule was evaporated spanning the monolayer to multilayer region. The molecular surface structure is investigated and the results indicate that no specific covalent chemical bonding is formed and that the plane formed by the different nitrogens in the HC molecules has a rather small angle versus the TiO2 substrate surface plane. Some molecular ordering also persists in the multilayer region. The experimental core level spectra, valence level spectra, and the N 1s x-ray absorption spectroscopy spectra are well modeled by calculations on an individual molecule. Interestingly, the formation of the TiO2∕HC interface results in significant binding energy shifts in core levels and valence levels shifting all peaks of a the HC material to the same extent. Smaller shifts were also observed in the substrate core level peaks. The shift is discussed in terms of nanoscale energy level bending and final state hole screening. With respect to electronic applications, specifically in a solid state dye-sensitized solar cell, it is argued that the observed energy level alignment at the TiO2∕HC interface can act as a hole trap.
Modulational instability of magnetosonic waves in a spin 1∕2 quantum plasma
Authors: Misra A. P. , Shukla P. K.
Published: May 2008

The modulational instability (MI) of magnetosonic waves (MSWs) is analyzed, by using a two-fluid quantum magnetohydrodynamic model that includes the effects of the electron-1∕2 spin and the plasma resistivity. The envelope modulation is then studied by deriving the corresponding nonlinear Schrödinger equation from the governing equations. The plasma resistivity is shown to play a dissipative role for the onset of MI. In the absence of resistivity, the microscopic spin properties of electrons can also lead to MI. In such a situation, the dominant spin contribution corresponds to a dense quantum plasma with the particle number density, n0≳1028m−3. Also, in such a dissipative (absorbing) medium, where the group velocity vector is usually complex for real values of the wave vector, the role of the real group velocity in the propagation of one-dimensional MSW packets in a homogeneous absorbing medium is reported. The effects of quantum spin on the stability/instability conditions of the magnetosonic envelope are obtained and examined numerically. From the nonlinear dispersion relation of the modulated wave packet it is found that the effect of the spin (plasma resistivity) is to decrease (increase) the instability growth rate provided the normalized Zeeman energy does not exceed a critical value. The theoretical results may have relevance to astrophysical (e.g., magnetars) as well as to ultracold laboratory plasmas (e.g., Rydberg plasmas).
Anisotropy of weak light scattering in thin opal films
Authors: Romanov Sergei G.
Published: May 2008

The forward and backward light scattering that accompanied the almost ballistic light propagation in opal-based three-dimensional photonic crystal (PhC) has been experimentally studied. The light path memory and the high anisotropy of scattering have been associated with low-order scattering at large-scale crystal defects. The strong backscattered light intensity has been linked to the uncoupled light at a PhC surface. The exponent of power-law approximation of angle diagrams of the scattered light intensity has been suggested as a measure of the scattering anisotropy. The scattering anisotropy spectra have demonstrated that in a vicinity to the first photonic bandgap, the lower directionality of the forward scattering is complemented by the higher directionality of the backward scattering.
Ordering and lyotropic behavior of a silicon-supported cationic and neutral lipid system studied by neutron reflectivity
Authors: Domenici F. , Castellano C. , Congiu A. , Pompeo G. , Felici R.
Published: May 2008

Self-assembling of amphipathic lipid films on solid support allows the structural investigation of important biological model systems, such as the vectorlike lipid membranes, in order to improve DNA transfection in nonviral gene therapy. We present a neutron reflectivity study of a binary lipid system composed of dioleoylphosphatidylcholine (DOPC) and dimethyldioctadecylammonium bromide (DDAB) deposited on [100] silicon support by means of spin coating technique. We underline their lyotropic behavior under saturated deuterium oxide (D2O) vapor thus pointing out that the lipid mixture is organized in ordered domains composed of plane lamellar bilayers of noninteractive DOPC and DDAB.
Interface formation and electronic structure of α-sexithiophene on ZnO
Authors: Blumstengel S. , Koch N. , Sadofev S. , Schäfer P. , Glowatzki H. , Johnson R. L. , Rabe J. P. , Henneberger F.
Published: May 2008

Interface formation between the organic semiconductor α-sexithiophene (6T) and polar as well as nonpolar ZnO surfaces is investigated. The growth mode of the organic layer is strongly influenced by the orientation of the ZnO surface. No indication for chemisorption of 6T on ZnO is found by photoelectron spectroscopy. The energy level alignment at the 6T/ZnO interface is of type-II facilitating electron transfer from the organic to the inorganic part and hole transfer in the other direction, rendering this heterostructure interesting for photovoltaic applications.
Effect of electron nonthermality on nonlinear electrostatic solitary waves in a charge varying dusty plasma
Authors: Tribeche Mouloud , Boumezoued Ghania
Published: May 2008

The effect of nonthermal electrons with excess of fast energetic electrons on large amplitude electrostatic solitary waves is investigated in a charge varying dusty plasma. The correct nonthermal electron charging is investigated based on the orbit-motion-limited approach. It is found that the nonlinear localized potential structure shrinks when the electrons deviate from isothermality. The dust particles are locally expelled and pushed out the region of the soliton localization as the electrons evolve far away from their thermodynamic equilibrium. Under certain conditions, the dust charge fluctuation may provide an alternate physical mechanism causing anomalous dissipation, the strength of which becomes important and may prevail over that of dispersion as the value of the electron nonthermal parameter α increases.
Hartree–Fock calculations with linearly scaling memory usage
Authors: Rudberg Elias , Rubensson Emanuel H. , Sałek Paweł
Published: May 2008

We present an implementation of a set of algorithms for performing Hartree–Fock calculations with resource requirements in terms of both time and memory directly proportional to the system size. In particular, a way of directly computing the Hartree–Fock exchange matrix in sparse form is described which gives only small addressing overhead. Linear scaling in both time and memory is demonstrated in benchmark calculations for system sizes up to 11 650 atoms and 67 204 Gaussian basis functions on a single computer with 32Gbytes of memory. The sparsity of overlap, Fock, and density matrices as well as band gaps are also shown for a wide range of system sizes, for both linear and three-dimensional systems.
Effects of channel geometry on buoyancy-driven mixing
Authors: Hallez Yannick , Magnaudet Jacques
Published: May 2008

The evolution of the concentration and flow fields resulting from the gravitational mixing of two interpenetrating miscible fluids placed in a tilted tube or channel is studied by using direct numerical simulation. Three-dimensional (3D) geometries, including a cylindrical tube and a square channel, are considered as well as a purely two-dimensional (2D) channel. Striking differences between the 2D and 3D geometries are observed during the long-time evolution of the flow. We show that these differences are due to those existing between the 2D and 3D dynamics of the vorticity field. More precisely, in two dimensions, the strong coherence and long persistence of vortices enable them to periodically cut the channels of pure fluid that feed the front. In contrast, in 3D geometries, the weaker coherence of the vortical motions makes the segregational effect due to the transverse component of buoyancy strong enough to preserve a fluid channel near the front of each current. This results in three different regimes for the front velocity (depending on the tilt angle), which is in agreement with the results of a recent experimental investigation. The evolution of the front topology and the relation between the front velocity and the concentration jump across the front are investigated in planar and cylindrical geometries and highlight the differences between 2D and 3D mixing dynamics.
Enhanced Hall effect in FexGe1−x nanocomposite films
Authors: Mi W. B. , Liu Y. W. , Jiang E. Y. , Bai H. L.
Published: May 2008

Enhanced Hall effect has been observed in the FexGe1−x nanocomposite films composed of nanoscale Fe grains embedded in amorphous Ge matrix. The Fe grain size, the saturation magnetization, and the interparticle interaction increase with increasing Fe atomic fraction x. The transport mechanism of the films changes from semiconducting to metallic character as x increases, and the percolation phenomenon ocurrs at x∼0.5. The Hall resistivity (ρxy) reaches its maximum of ∼126μΩcm at x=0.5, which is ∼140 times larger than that of Fe films. The ordinary and extraordinary Hall coefficients are enhanced by two orders in magnitude compared to pure Fe films and four orders compared to the bulk Fe. Upon annealing at 400°C, the enhanced Hall effect disappears with the disappearance of the Fe grains. This enhanced Hall effect can be attributed to the local quantum interference effect due to the presence of ∼1–2nm Fe grains.
Electronic structure of a laterally graded ZrO2–TiO2 film on Si(100) prepared by metal-organic chemical vapor deposition in ultrahigh vacuum
Authors: Richter J. H. , Karlsson P. G. , Sandell A.
Published: May 2008

A TiO2–ZrO2 film with laterally graded stoichiometry has been prepared by metal-organic chemical vapor deposition in ultrahigh vacuum. The film was characterized in situ using synchrotron radiation photoelectron spectroscopy (PES) and x-ray absorption spectroscopy. PES depth profiling clearly shows that Ti ions segregate toward the surface region when mixed with ZrO2. The binding energy of the ZrO2 electronic levels is constant with respect to the local vacuum level. The binding energy of the TiO2 electronic levels is aligned to the Fermi level down to a Ti∕Zr ratio of about 0.5. At a Ti∕Zr ratio between 0.1 and 0.5, the TiO2 related electronic levels become aligned to the local vacuum level. The addition of small amounts of TiO2 to ZrO2 results in a ZrO2 band alignment relative to the Fermi level that is less asymmetric than for pure ZrO2. The band edge positions shift by −0.6eV for a Ti∕Zr ratio of 0.03. This is explained in terms of an increase in the work function when adding TiO2, an effect that becomes emphasized by Ti surface segregation.
Fabrication and characterization of metal-ferroelectric (PbZr0.53Ti0.47O3)-Insulator (Y2O3)-semiconductor field effect transistors for nonvolatile memory applications
Authors: Shih Wen-Chieh , Juan Pi-Chun , Lee Joseph Ya-min
Published: May 2008

Metal-ferroelectric-insulator-semiconductor (MFIS) field effect transistors with Pb(Zr0.53,Ti0.47)O3 (PZT) ferroelectric layer and yttrium oxide Y2O3 insulator layer were fabricated. The maximum C-V memory window of 1.5V was obtained at a sweep voltage of 8V. The dominating conduction mechanism through the MFIS structure is Schottky emission in the temperature range from 300to450K. The nonvolatile operation of MFIS transistors was demonstrated by applying positive/negative writing pulses. The retention shows that the transistors maintain a threshold voltage window of 1.2V without deterioration after 3×103s. The low leakage current and the high effective Y2O3∕Si barrier height of 1.85eV can well explain the size of memory window and retention properties. The effect of charge injection is reduced in this structure.