bluuebunny/crossref_metadata_2025 huggingface dataset:
Biophysics of viral infectivity: matching genome length with capsid size
Authors: Nurmemmedov Elmar , Castelnovo Martin , Catalano Carlos Enrique , Evilevitch Alex
Published: April 2008

In this review, we discuss recent advances in biophysical virology, presenting experimental and theoretical studies on the physical properties of viruses. We focus on the double-stranded (ds) DNA bacteriophages as model systems for all of the dsDNA viruses both prokaryotic and eukaryotic. Recent studies demonstrate that the DNA packaged into a viral capsid is highly pressurized, which provides a force for the first step of passive injection of viral DNA into a bacterial cell. Moreover, specific studies on capsid strength show a strong correlation between genome length, and capsid size and robustness. The implications of these newly appreciated physical properties of a viral particle with respect to the infection process are discussed.
Rob Amery, ‘Warrabarna Kaurna!’
Reclaiming an Australian language. (Multilingualism and
Linguistic Diversity 1). Lisse, The Netherlands: Swets &
Zeitlinger, 2000. Pp. xx, 289. Hb $63.00.
Authors: Loether Christopher
Published: April 2008

Many linguists believe that the revitalization
of moribund languages, where there may only be a handful of
elderly fluent speakers left, is a noble – if perhaps
nearly impossible – ideal for native communities involved
in such work. Even more challenging is the reintroduction of
a long-dead language such as the South Australian language Kaurna
(pronounced [ga:na]), spoken on the Adelaide plains
until the last native speaker, Ivaritji (a.k.a. Amelia Taylor),
died in 1929. Rob Amery challenges the standards by which language
revitalization programs are judged as successful, while giving
us a step-by-step method for the reintroduction and revalorization
of an extinct native tongue, which he calls the Formulaic Method.
This detailed case study of what is, after all, just the beginning
stages of Kaurna language revival will be of interest not just
to linguists involved in the field, but especially to community
members and other nonspecialists who are somehow connected with
lesser-used languages and language revival efforts. Amery's
work is also an important contribution to the emerging field
of ecological linguistics and its application to language
planning.
Dialect accommodation in a bi-ethnic mountain enclave community:
More evidence on the development of African American English
Authors: MALLINSON CHRISTINE , WOLFRAM WALT
Published: April 2008

The investigation of isolated African American
enclave communities has been instrumental in reformulating the
historical reconstruction of earlier African American English
and the current trajectory of language change in African American
Vernacular English (AAVE). This case study examines a unique
enclave sociolinguistic situation – a small, long-term,
isolated bi-ethnic enclave community in the mountains of western
North Carolina – to further understanding of the role
of localized dialect accommodation and ethnolinguistic
distinctiveness in the historical development of African American
English. The examination of a set of diagnostic phonological
and morphosyntactic variables for several of the remaining African
Americans in this community supports the conclusion that earlier
African American English largely accommodated local dialects
while maintaining a subtle, distinctive ethnolinguistic divide.
However, unlike the situation in some other African American
communities, there is no current movement toward an AAVE external
norm for the lone isolated African American teenager; rather,
there is increasing accommodation to the local dialect.
Contact-based, identity-based, and ideologically based explanations
are appealed to in describing the past and present direction
of change for the African Americans in this receding community.
Précis of How Children Learn the Meanings of Words
Authors: Bloom Paul
Published: April 2008

Normal children learn tens of thousands of words, and do so quickly and efficiently, often in highly impoverished environments. In How Children Learn the Meanings of Words, I argue that word learning is the product of certain cognitive and linguistic abilities that include the ability to acquire concepts, an appreciation of syntactic cues to meaning, and a rich understanding of the mental states of other people. These capacities are powerful, early emerging, and to some extent uniquely human, but they are not special to word learning. This proposal is an alternative to the view that word learning is the result of simple associative learning mechanisms, and it rejects as well the notion that children possess constraints, either innate or learned, that are specifically earmarked for word learning. This theory is extended to account for how children learn names for objects, substances, and abstract entities, pronouns and proper names, verbs, determiners, prepositions, and number words. Several related topics are also discussed, including naïve essentialism, children's understanding of representational art, the nature of numerical and spatial reasoning, and the role of words in the shaping of mental life.
Robotic search: What's in it for comparative cognition?
Authors: De Lillo Carlo
Published: April 2008

Although the advantage of biorobotics over traditional modelling tools is not always evident from the studies on animal search addressed in the target article, this commentary argues that testing different robotic architectures and specific biological organisms in structured search spaces, where environmental constraints matter, might prove one of the most promising research strategies in comparative cognition.
Vocabulary and general intelligence
Authors: Jensen Arthur R.
Published: April 2008

Acquisition of word meanings, or vocabulary, reflects general mental ability (psychometric g) more than than do most abilities measured in test batteries. Among diverse subtests, vocabulary is especially high on indices of genetic influences. Bloom's exposition of the psychological complexities of understanding words, involving the primacy of concepts, the theory of mind, and other processes, explains vocabulary's predominant g saturation.
An intentional dynamics approach to comparing robots with their biological targets
Authors: Effken Judith A. , Shaw Robert E.
Published: April 2008

After identifying similarities in the paradigmatic problems of biorobotics and ecological psychology, we suggest a way to compare the performance of robots with that of their biological targets. The crucial comparison is between the intentional dynamics of the robot and those of the targeted animal, a measure that depends critically on recognizing and describing the underlying affordance-effectivity match of the target system.
Fast-mapping children vs. slow-mapping adults: Assumptions about words and concepts in two literatures
Authors: Murphy Gregory L.
Published: April 2008

Research on children's and adults' concepts embodies very different assumptions of how concepts are structured, as reflected in their experimental designs. Developmental studies seem to assume that categories contain highly similar objects that can all be identified from one or two examples. If concepts are more like those tested in adult experiments, research on word learning may be misleading.
There is more to biological behavior than causation and control
Authors: Krause Mark A.
Published: April 2008

Biorobots may model the causation of relatively simple behaviors, but many animal behaviorists are concerned with complex cognitive traits and their evolution. Biorobotics seems limited in its ability to model cognition and to provide evolutionary explanations. Also, if robots could model complex traits, such as theory of mind, underdetermination could be problematic. Underdetermination is also a challenge for comparative psychologists.
Like the perfect animal, there's no such thing as the perfect institution
Authors: Lohmann Susanne
Published: April 2008

Models of biological and political systems share in common an irreconcilable tension. They must extract the essential features of the system to make its workings comprehensible to the human observer, and yet the omitted underbrush is essential to the workings of the system. A good model accommodates both the workings of the system and the cognitive makeup of the observer.
Differentiating robotic behavior and artificial intelligence from animal behavior and biological intelligence: Testing structural accuracy
Authors: Miller Ralph R. , Arcediano Francisco
Published: April 2008

We emphasize the feature of Webb's presentation that bears most directly on contemporary research with real animals. Many neuroscience modelers erroneously conclude that a model that performs like an animal must have achieved this goal through processes analogous with those used by the animal. A simulation failure justifies rejecting a model, but success does not justify acceptance. However, an important benefit of models, successful or otherwise, is to stimulate new research.
Rational statistical inference: A critical component for word learning
Authors: Xu Fei , Tenenbaum Joshua B.
Published: April 2008

In order to account for how children can generalize words beyond a very limited set of labeled examples, Bloom's proposal of word learning requires two extensions: a better understanding of the “general learning and memory abilities” involved, and a principled framework for integrating multiple conflicting constraints on word meaning. We propose a framework based on Bayesian statistical inference that meets both of those needs.
Robotic modeling of mobile ball-catching as a tool for understanding biological interceptive behavior
Authors: Sugar Thomas , McBeath Michael
Published: April 2008

We support Webb's insights into the potential benefits of using robotic modeling to better understand biological behavior. We defend the major points put forward by Webb by presenting a specific case study in which robotic modeling of mobile ball catching has helped refine and clarify aspects of our understanding of biological interceptive behavior.
Addressing semantics promotes the development of reading fluency
Authors: BERENDS INEZ E. , REITSMA PIETER
Published: April 2008

In two experimental training studies we examined the hypothesis that an emphasis on the meaning of a word is more effective than merely focusing on the orthography to increase reading fluency. Reading delayed children from Grade 1 (mean age = 7.3 years) and two groups from Grade 2 (mean age = 8.3 and 7.8 years) repeatedly read words while focusing either on the orthography or on the semantics of the word. Furthermore, the claim that limited exposure duration during training further promotes fluency was examined. The results show that the semantic based exercises yield more effect than orthographic training, especially for Grade 2 students. No beneficial effect is found for limited presentation duration. The results strongly suggest that practice with printed words with a specific focus on the semantic characteristics effectively promotes the attainment of reading fluency.
The role of phonological storage deficits in specific language impairment: A reconsideration
Authors: Weismer Susan Ellis , Edwards Jan
Published: April 2008

In her Keynote Article, Gathercole (2006) presents a theoretical framework intended to account for evidence regarding the relation between nonword repetition and word learning. This framework stems from an impressive amount and breadth of research on this topic, including findings from adults and children with typical language abilities as well as language learning disorders. In this commentary we focus on claims relative to the interpretation of nonword repetition deficits in children with specific language impairment (SLI). One issue we address pertains to the nature of the proposed model of nonword processing and word learning, particularly with respect to phonological sensitivity and storage. The second issue we address relates to the assumption that a phonological storage deficit, although not sufficient, is necessary for SLI.
Commentary on Keynote
Authors: Gray Shelley
Published: April 2008

Our understanding the relationship between verbal short-term memory as indexed by nonword repetition and word learning must now incorporate myriad factors that were not as apparent 17 years ago when Gathercole and Baddeley (1989) proposed that “the phonological memory skills tapped by nonword repetition play a causal role in vocabulary development” (p. 211). In particular, successful nonword repetition involves more than the phonological loop, word learning happens by degrees, and is influenced by many factors other than phonology, and children with specific language impairment (SLI), who have served as test cases by virtue of consistently demonstrating phonological memory deficits, often exhibit other deficits with the potential to negatively impact word learning. Gathercole (2006) still makes the case for temporary phonological storage playing an important role in word learning, but with several caveats. I would like to add two.
Nonword repetition, phonological storage, and multiple determinations
Authors: Gupta Prahlad
Published: April 2008

The proposals that (a) nonword repetition and word learning both rely on phonological storage and (b) both are multiply determined are two of the major foci of Gathercole's (2006) Keynote Article, which marshals considerable evidence in support of each. In my view, the importance of these proposals cannot be overstated: these two notions go to the heart of the relationship between nonword repetition and word learning. Indeed, they figure prominently in the approach that my colleagues and I have taken to studying that relationship (e.g., Gupta, 2006; Gupta, Lipinski, Abbs, & Lin, 2005; Gupta & MacWhinney, 1997). An important aspect of our approach has been the attempt to construct a computational model that can simulate performance in a nonword repetition task and in a word learning task, the rationale being that a computational model that achieved this would constitute a proposal about the processing mechanisms that may underlie the relationship. In this Commentary, I describe how our computational work offers a concrete way of thinking about how nonword repetition and word learning may rely on phonological storage, and about how these abilities may be multiply determined. Such computational work is, I suggest, a valuable tool in further investigating the important relationship that has been revealed by Gathercole's influential work, and that is analyzed in the Keynote Article.
Nonword repetition and levels of abstraction in phonological knowledge
Authors: Munson Benjamin
Published: April 2008

Susan Gathercole's Keynote Article (2006) is an impressive summary of the literature on nonword repetition and its relationship to word learning and vocabulary size. When considering research by Mary Beckman, Jan Edwards, and myself, Gathercole speculates that our finding of a stronger relationship between vocabulary measures and repetition accuracy for low-frequency sequences than for high-frequency sequences is due to differences in the range of the two measures. In our work on diphone repetition (e.g., Edwards, Beckman, & Munson, 2004; Munson, Edwards, & Beckman, 2005) we tried to increase the range in our dependent measures by coding errors on a finer grained scale than simple correct/incorrect scoring would allow. Moreover, restriction of range does not appear to be the driving factor in the relationship between vocabulary size and the difference between high- and low-frequency sequence repetition accuracy (what we call the frequency effect) in at least one of our studies (Munson et al., 2005). When the children with the 50 lowest mean accuracy scores for high-frequency sequences were examined, vocabulary size accounted for 10.5% of the variance in the frequency effect beyond what was accounted for by chronological age. When the 50 children with the highest mean accuracy scores for high-frequency sequences were examined (a group in which the range of high-frequency accuracy scores was more compressed, arguably reflecting ceiling effects), an estimate of vocabulary size accounted for only 6.9% of the frequency effect beyond chronological age. The associated β coefficient was significant only at the α<0.08 level. This is the opposite pattern than Gathercole's argument would predict.
Exploring the impact of higher level linguistic representations on nonword repetition performance
Authors: van der Lely Heather K. J. , Gallon Nichola
Published: April 2008

Gathercole's (2006) comprehensive and interesting Keynote Article on the nature of the relations between nonword repetition and word learning highlights the complex number of interacting factors that affect this relation through development. In this Commentary we focus on the impact of higher level cognition, particularly linguistic representations on lower level functions such as attention and processing, as well as higher level functions such as memory. In addition, we note the importance of distinguishing children with specific language impairment (SLI) who do and do not have phonological deficit when testing for memory impairments. We argue that further detailed investigations are warranted at the linguistic levels of cognitive processing alongside memory tasks that tap different components of language and nonlinguistic memory. Such studies would help tease apart the complex, and probably bidirectional relations between attention, memory, and linguistic representations. Moreover, we propose that this investigative strategy crucially needs to take a longitudinal developmental perspective if we are to understand the developmental trajectory.
Learning prosody and fluency characteristics of second language speech: The effect of experience on child learners' acquisition of five suprasegmentals
Authors: TROFIMOVICH PAVEL , BAKER WENDY
Published: April 2008

This study examined second language (L2) experience effects on children's acquisition of fluency-(speech rate, frequency, and duration of pausing) and prosody-based (stress timing, peak alignment) suprasegmentals. Twenty Korean children (age of arrival in the United States = 7–11 years, length of US residence = 1 vs. 11 years) and 20 age-matched English monolinguals produced six English sentences in a sentence repetition task. Acoustic analyses and listener judgments were used to determine how accurately the suprasegmentals were produced and to what extent they contributed to foreign accent. Results indicated that the children with 11 years of US residence, unlike those with 1 year of US residence, produced all but one (speech rate) suprasegmentals natively. Overall, findings revealed similarities between L2 segmental and suprasegmental learning.
The comprehension of Turkish relative clauses in second language acquisition and agrammatism
Authors: AYDIN ÖZGÜR
Published: April 2008

The purposes of this study are to test whether the processing of subject relative (SR) clauses is easier than that of object relative (OR) clauses in Turkish and to investigate whether the comprehension of SRs can be better explained by the linear distance hypothesis or structural distance hypothesis (SDH). The question is examined in two groups of second language (L2) learners of different proficiency levels and a few agrammatics expected to show a similar pattern. Each participant is asked to comprehend 15 sentences containing SRs and ORs via a picture selection task. The results indicate that comprehension of SRs is easier than that of ORs for intermediate level L2 learners, whereas there is no significant difference between the types of relative clauses for early learners. Another result is that early learners produce errors similar to those of agrammatics, which are explained through trace deletion and referential strategy. These findings on Turkish provide significant support for the SDH.
Geometric thermodynamic formalism and real analyticity for meromorphic functions of finite order
Authors: MAYER VOLKER , URBAŃSKI MARIUSZ
Published: April 2008

Working with well chosen Riemannian metrics and employing Nevanlinna’s theory, we make the thermodynamic formalism work for a wide class of hyperbolic meromorphic functions of finite order (including in particular exponential family, elliptic functions, cosine, tangent and the cosine–root family and also compositions of these functions with arbitrary polynomials). In particular, the existence of conformal (Gibbs) measures is established and then the existence of probability invariant measures equivalent to conformal measures is proven. As a geometric consequence of the developed thermodynamic formalism, a version of Bowen’s formula expressing the Hausdorff dimension of the radial Julia set as the zero of the pressure function and, moreover, the real analyticity of this dimension, is proved.
Smoothness is not an obstruction to realizability
Authors: WINDSOR A. J.
Published: April 2008

A sequence of non-negative integers$(\phi _n)_{n =1}^\infty $is said to berealizableif there is a mapTof a setXsuch that ϕn=#{x:Tnx=x}. We prove that any realizable sequence can be realized by a$C^\infty $diffeomorphism of$\mathbb {T}^2$.
A Multinational and its Labor Force: The Dutch East India Company, 1595–1795
Authors: Lucassen Jan
Published: April 2008

This essay focuses on the emergence of an international labor market connecting Europe with southern Africa and south and southeast Asia, showing the intertwining of commercialization and proletarianization in the institution that created and coordinated perhaps the most important international labor market connecting Europe to the Far East.
Spaniards on the Silver Roll: Labor Troubles and Liminality in the Panama Canal Zone, 1904–1914
Authors: Greene Julie
Published: April 2008

This article examines the experiences of Spanish workers during the construction of the Panama Canal by the United States from 1904 to 1914. Spaniards engaged in a wide range of protest actions during the construction years, from strikes to food riots to anarchist politics. Employing Victor Turner's concept of liminality, the article highlights the mutability of the Spaniards' position and identity and examines several factors that shaped their experiences: the US government's policies of racial segregation and the injustices Spaniards experienced; the political and racial identities they brought with them from Spain; and their complex racial and imperial status in the Canal Zone. Spaniards possessed a remarkably fluid racial identity, considered white or nonwhite depending on circumstances, and that shifting status fueled their racial animosities as well as their protests.
The Essential E.P. Thompson, edited by Dorothy Thompson. New Press: New York, 2001. x + 498 pp. $45.00 cloth; $21.95 paper.
Authors: Linebaugh Peter
Published: April 2008

For Aristotle identifying the essence of something was a step to its classification, and thus the genre to which it belonged. For Leibniz every individual thing had an essence, and thus it established specific difference. Who was the essential E.P. Thompson, one of a kind or a type? The vogue in America was to speak of the British Marxist historians, or English social history as a genre.
The Essential E.P. Thompson, edited by Dorothy Thompson. New Press: New York, 2001. x + 498 pp. $45.00 cloth; $21.95 paper.
Authors: Palmer Bryan D.
Published: April 2008

E.P. Thompson was nursed on a mother's milk of transatlantic missionary work and writings on the Middle East that reached back to the last half of the nineteenth century. Fathered on Bengali literature, the poetry of the Great War, cricket with the likes of Nehru, and the struggle for Indian independence, Thompson was born into a highly literate and deeply politicized global village. Small wonder that at seventeen he was an anti-fascist and a soldier. But he took a wide Left turn, following in a brother's footsteps, to become a Marxist and a Communist in his twenties, only to find himself, by 1956, donning dissident dress, leading an exodus from the Communist Party of Great Britain, building a revolutionary New Left in the seemingly unpropitious climate of the late 1950s.
Boys Will Be Boys: Working-Class Masculinities in the Age of Mass Production
Authors: Heron Craig
Published: April 2008

This article investigates the changing construction of masculine identities among working-class males in a large Canadian factory city, Hamilton, Ontario, in the half century before the Second World War. It argues that, long before individual working men embraced the patriarchal identity of breadwinner and head of family, they had learned and practiced how to be “masculine” in family homes, schools, city streets, workplaces, and pleasure sites. The result was a complex bundle of contradictory attitudes and practices in which the processes of class, ethnic/racial, and gender formation were closely interwoven and in which the male body became a crucial vehicle for expressing gender. The article stresses that working-class masculinities were not fixed, static, or universal, but shaped in specific ways in different contexts and subject to challenges and re-negotiation over time. In the period under study here, working-class males faced new forms of institutional regulation in schools, workplaces, streets, and military trenches, the commercialization of many of their pleasures, and new independence and assertiveness in the pubic sphere among the women of their communities. Negotiating these challenges brought both continuities and significant changes in masculine identities.
Race and the Construction of Working-Class Masculinity in the Nigerian Coal Industry: The Initial Phase, 1914–1930
Authors: Brown Carolyn
Published: April 2008

This article examines the impact of the capitalist economy, colonial rule, and wage labor on African masculinity and how African ideas about manhood impacted behavior and expectations of work in the coal mines of the Enugu Government Colliery in southeastern Nigeria from 1914 until the great depression. These mines were a “site” where racism became a crucial part of British strategies to control African labor and is one of the first places African workers experienced the “colonial masculinity” of racist white bosses. Both the workplace and the development of the city of Enugu encouraged subordinate local men (local slaves, unmarried men, poor men) to challenge the hegemony of powerful elite rural men in the form of rural revolts by men pressed into the mines and waves of industrial protest against conditions in the mines. Coalminers' presence in and political ties to rural villages led them to push for increased wages used to enhance their standing as men in their communities. Also, both the material and ritual requirements of rural male status and the masculine ethos of coalmining figured critically in workers' assessments of a “just” wage and respectful working conditions. Finally, miners drew strength from their position as “modern,” self-improving rural men to challenge racist (the African “boy”) and emasculating treatment in the mines. At the same time working men drew strength from their jobs in a “modern” industry (and the income they generated) to challenge the power of authoritarian colonial chiefs and elite men in the rural village. The article suggests that by factoring race and masculinity into the analysis of African laboring men scholars can gain new insights into the consciousness of workers.
Desirable Dress: Rosies, Sky Girls, and the Politics of Appearance
Authors: Boris Eileen
Published: April 2008

Desirable dress on the job, whether pants, sweaters, or mini-skirted uniforms, contains symbolic meaning, but whose sexual subjectivity it expresses is not always clear. Appearance may be a proxy for other forms of contestation or just be a conveyer of pleasure that makes work just a little more humane. This essay rethinks two cases where issues of self-fashioning, appearance, sexuality, employer strictures, and state policy intertwined: the shop floors of the Second World War and the flight cabins of postwar airlines: the first, male dominated manufacturing in which women labored “for the duration”; the second, a prototypical female service industry in which fierce competition led to selling sexual allure along with comfort and safety. However mediated, voices of wage-earning women in both the 1940s and 1960s announced new expectations of womanhood, beauty, and sexual expressiveness. But while management attempted to suppress women's bodies in the shipyards and other wartime workplaces, by the 1960s airlines promoted the body of the flight attendant. In both examples, state mediation—through sources available as well as actual public policies—complicates our attempt to unravel pleasure and constraint in dressing, grooming, and sexual presence on the job. Whether or not dress requirements disciplined employee bodies, served as a guarantee of efficiency or a check against accidents and the expense of worker compensation, or opened new possibilities for sexual or gendered identities was hardly predetermined. Employers could demand slacks, women could wear them, but what dress was desirable varied with the beholder.
Masculinity, the Embodied Male Worker, and the Historian’s Gaze
Authors: Baron Ava
Published: April 2008

While historians have provided insights into the ways women's work culture and labor organizing were infused with issues of sex, sexuality and appearance, they have not similarly examined the white male working body. This article discusses the significance of this different analysis for our understanding of men workers and for its ability to continue to marginalize women at the workplace. It considers how to incorporate the “bodily turn” in history by examining three conceptual themes in research on working-class masculinity: masculinity crises, muscular masculinity, and homosociality.
Diagnostic potential of advanced X-ray spectroscopy for
investigation of hot dense plasmas
Authors: RENNER O. , USCHMANN I. , FÖRSTER E.
Published: April 2008

Modern experimental methods and instruments for X-ray spectral
investigation of hot dense plasma provide complex information on
environmental conditions in extreme states of matter. The basic
spectroscopic conceptions for K-shell plasma diagnosis are
outlined, the main characteristics of toroidally bent crystal
spectrometers and vertical-dispersion instruments are briefly reviewed.
Selected applications (monitoring and optimization of the emission from
the femtosecond-laser-produced plasmas, characterization of colliding
laser-exploded foils, spectral line merging, and continuum lowering in
constrained-flow plasmas) demonstrate the usefulness of advanced
spectroscopic methods for plasma diagnostics and fundamental
research.
Hydrodynamics of plasma and shock waves generated by the high-power
GARPUN KrF laser
Authors: ZVORYKIN V.D. , BAKAEV V.G. , LEBO I.G. , SYCHUGOV G.V.
Published: April 2008

The electron-beam-pumped KrF laser installation GARPUN with a 100-J
output energy and long 100-ns pulse duration has been used to
investigate laser–target interactions in a broad range of laser
intensities for small (150 μm) and large (∼1 cm) irradiated
spots. For higher intensities (up to 5 × 1012
W/cm2), a conical shock wave was generated in condensed
matter by megabar pressure at the ablation front. It propagated with a
supersonic velocity in a quasisteady manner together with a conical
shock wave inside a target. Evaporated target material moving with a
velocity of ∼50 km/s formed an extended plasma corona of ∼5
mm length with an electron temperature of ∼100 eV. Emission spectra
of plasma have been investigated in the extreme UV range 120–250
Å. For lower intensities (108–109
W/cm2), planar shock waves in normal density air were
produced with initial velocities up to 4 km/s in the forward
direction and 7 km/s in the opposite direction toward incident
radiation. In rarefied air, the forward shock wave kept velocities
constant whereas the backward ones were accelerated up to 30 km/s.
Planar compression waves in transparent condensed matter were also
demonstrated propagating with sonic velocity.
Parametric up-conversion of a trivelpiece–gould mode in a
beam–plasma system
Authors: GUPTA D.N. , SHARMA A.K.
Published: April 2008

A large amplitude Trivelpiece–Gould (TG) mode, in a strongly
magnetized beam–plasma system, parametrically couples to a beam
space charge mode and a TG mode sideband. The density perturbation
associated with the beam mode couples with the electron oscillatory
velocity, due to the pump wave, to produce a nonlinear current, driving
the sideband. The pump and the sideband waves exert a ponderomotive
force on the electrons with a component parallel to the ambient
magnetic field, driving the beam mode. For a pump wave having
k0·v0b0/ω0
< 0, where ω0, k0 are the
frequency and the wave number of the pump, and
v0b0 is the beam velocity, the
sideband is frequency upshifted. At low beam density (Compton regime)
the growth rate of the parametric instability scales as two-thirds
power of the pump amplitude, and one-third power of beam density. In
the Raman regime, the growth rate scales as half power of beam density
and linearly with pump amplitude. The background plasma has a
destabilizing role on the instability.
Characterization of a bright, tunable, ultrafast Compton scattering X-ray source
Authors: HARTEMANN F.V. , TREMAINE A.M. , ANDERSON S.G. , BARTY C.P.J. , BETTS S.M. , BOOTH R. , BROWN W.J. , CRANE J.K. , CROSS R.R. , GIBSON D.J. , FITTINGHOFF D.N. , KUBA J. , LE SAGE G.P. , SLAUGHTER D.R. , WOOTTON A.J. , HARTOUNI E.P. , SPRINGER P.T. , ROSENZWEIG J.B. , KERMAN A.K.
Published: April 2008

The Compton scattering of a terawatt-class, femtosecond laser pulse by a high-brightness, relativistic electron beam has been demonstrated as a viable approach toward compact, tunable sources of bright, femtosecond, hard X-ray flashes. The main focus of this article is a detailed description of such a novel X-ray source, namely the PLEIADES (Picosecond Laser–Electron Inter-Action for the Dynamical Evaluation of Structures) facility at Lawrence Livermore National Laboratory. PLEIADES has produced first light at 70 keV, thus enabling critical applications, such as advanced backlighting for the National Ignition Facility andin situtime-resolved studies of high-Zmaterials. To date, the electron beam has been focused down to σx= σy= 27 μm rms, at 57 MeV, with 266 pC of charge, a relative energy spread of 0.2%, a normalized horizontal emittance of 3.5 mm·mrad, a normalized vertical emittance of 11 mm·mrad, and a duration of 3 ps rms. The compressed laser pulse energy at focus is 480 mJ, the pulse duration 54 fs Intensity Full Width at Half-Maximum (IFWHM), and the 1/e2radius 36 μm. Initial X rays produced by head-on collisions between the laser and electron beams at a repetition rate of 10 Hz were captured with a cooled CCD using a CsI scintillator; the peak photon energy was approximately 78 keV, and the observed angular distribution was found to agree very well with three-dimensional codes. The current X-ray dose is 3 × 106photons per pulse, and the inferred peak brightness exceeds 1015photons/(mm2× mrad2× s × 0.1% bandwidth). Spectral measurements using calibrated foils of variable thickness are consistent with theory. Measurements of the X-ray dose as a function of the delay between the laser and electron beams show a 24-ps full width at half maximum (FWHM) window, as predicted by theory, in contrast with a measured timing jitter of 1.2 ps, which contributes to the stability of the source. In addition,K-edge radiographs of a Ta foil obtained at different electron beam energies clearly demonstrate the γ2-tunability of the source and show very good agreement with the theoretical divergence-angle dependence of the X-ray spectrum. Finally, electron bunch shortening experiments using velocity compression have also been performed and durations as short as 300 fs rms have been observed using coherent transition radiation; the corresponding inferred peak X-ray flux approaches 1019photons/s.
An ensemble of new techniques to study soft-X-ray-induced variations in cellular metabolism
Authors: TURCU EDMOND , ALLOT RICK , LISI NICOLA , BATANI DIMITRI , BORTOLOTTO FULVIA , MASINI ALESSANDRA , MILANI MARZIALE , BALLERINI MONICA , FERRARO LORENZO , POZZI ACHILLE , PREVIDI FABIO , REBONATO LORENZO
Published: April 2008

An ensemble of new techniques has been developed to study cell metabolism. These include: CO2production monitoring, cell irradiation with soft X rays produced with a laser-plasma source, and study of oscillations in cell metabolic activity via spectral analysis of experimental records. Soft X-rays at about 0.9 keV, with a very low penetration in biological material, were chosen to produce damages at the metabolic level, without great interference with DNA activity. The use of a laser-plasma source allowed a fast deposition of high doses. Monitoring of CO2production allowed us to measure cell metabolic response immediately after irradiation in a continuous and noninvasive way. Also a simple model was developed to calculate X-ray doses delivered to the different cell compartments following a Lambert–Bouguet–Beer law. Results obtained onSaccharomyces cerevisiaeyeast cells in experiments performed at Rutherford Appleton Laboratory are presented.
The SPARC/X SASE-FEL Projects
Authors: ALESINI D. , BERTOLUCCI S. , BIAGINI M.E. , BONI R. , BOSCOLO M. , CASTELLANO M. , CLOZZA A. , DI PIRRO G.. , DRAGO A. , ESPOSITO A. , FERRARIO M. , FUSCO V. , GALLO A. , GHIGO A. , GUIDUCCI S. , INCURVATI M. , LIGI C. , MARCELLINI F. , MIGLIORATI M. , MILARDI C. , MOSTACCI A. , PALUMBO L. , PELLEGRINO L. , PREGER M. , RAIMONDI P. , RICCI R. , SANELLI C. , SERIO M. , SGAMMA F. , SPATARO B. , STECCHI A. , STELLA A. , TAZZIOLI F. , VACCAREZZA C. , VESCOVI M. , VICARIO C. , ZOBOV M. , ALESSANDRIA F. , BACCI A. , BOSCOLO I. , BROGGI F. , CIALDI S. , DE MARTINIS C. , GIOVE D. , MAROLI C. , PETRILLO V. , ROMÈ M. , SERAFINI L. , MUSUMECI P. , MATTIOLI M. , CATANI L. , CHIADRONI E. , TAZZARI S. , CIOCCI F. , DATTOLI G. , DORIA A. , FLORA F. , GALLERANO G.P. , GIANNESSI L. , GIOVENALE E. , MESSINA G. , MEZI L. , OTTAVIANI P.L. , PICARDI L. , QUATTROMINI M. , RENIERI A. , RONSIVALLE C. , CIANCHI A. , SCHAERF C. , ROSENZWEIG J.B.
Published: April 2008

SPARC and SPARX are two different initiatives toward an ItalianFreeElectronLaser (FEL) source operating in theSelfAmplifiedSpontaneousEmission (SASE) mode, in which several national research institutions are involved. SPARC is a high gain FEL project devoted to provide a source of visible and VUV radiation while exploiting the SASE mechanism. An advanced Photo-Injector system, emittance compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, (∼500 nm). The production of flat top drive laser beams, high peak current bunches, and emittance compensation scheme will be investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution of such a high gain SASE FEL toward the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. To get the required value for the bunch peak current, Ipeak≈ 2.5 kA, the “hybrid” scheme, RF-compression stage plus magnetic chicane, is analyzed and compared with the more standard double stage of magnetic compression. The two options are reviewed considering the tolerance to the drive laser pulse phase jitter.
Chirped-pulse oscillators for the generation of high-energy
femtosecond laser pulses
Authors: FUERBACH ALEXANDER , FERNANDEZ A. , APOLONSKI A. , FUJI T. , KRAUSZ F.
Published: April 2008

This paper reports on a novel approach for producing high energy
femtosecond pulses without external amplification. The so-called
chirped-pulse oscillator (CPO) concept is based on an extended-cavity
oscillator, operating at small net positive intracavity group delay
dispersion (GDD), over a broad spectral range by the use of chirped
multilayer mirrors. The resultant chirped picosecond pulses are compressed
by a dispersive delay line external to the laser cavity. Utilizing this
technique, sub-30 fs pulses with an energy exceeding 200 nJ at a
repetition rate of 11 MHz were produced. The demonstrated peak power in
excess of 5 MW is the highest ever achieved from a cw-pumped laser and is
expected to be scaleable to tens of megawatts by increasing the pump power
and/or decreasing the repetition rate. The demonstrated source allows
micromachining of any materials under relaxed focusing conditions.
Propagation of intense plasma and ion beams across B-field in vacuum
and magnetized plasma
Authors: ANDERSON M. , GARATE E. , ROSTOKER N. , SONG Y. , VAN DRIE A. , BYSTRITSKII VITALY
Published: April 2008

This paper summarizes experimental results on the injection and
transport of intense, wide cross-section H+ plasma (PB), and
ion beams (IB), in vacuum and ambient H+ plasma across an
applied B-field. The injection of plasma and ion beams into magnetic
confinement devices have the potential to heat and support current in
these systems (e.g., field-reversed configurations). The translational
energies of the PB and IB ranged between Epb = 60 to
120 eV and EIB = 60 to 120 keV, with temperatures and
densities in the range of Tb ∼ 2 to 10 eV,
nb ∼ 1012 to 1013
cm−3, and Tb ∼ 200 eV,
nb 1010 to 1011
cm−3, respectively. Compared to earlier studies (Peter et al., 1979; Wessel et al.,
1988, 1990), this
research extends the experimental parameter space to higher beam current
densities (up to 30 A/cm2) and higher B-field strengths up
to 1.6 kG. The PB and IB were both about 10 cm in diameter at the
injection port, and the ratio of beam specific energy to ambient B-field
specific energy, β, was in the range of 0.1 to 10. Ratios of beam
Larmor radius to beam size, ρ, ranged from 10−1 to 1
and 1 to 10 for the PB and IB, respectively. Cross B-field propagation of
the PB in vacuum was undeflected as a whole with a sharp increase (one
order or more) in the current density of the central beam core at B-field
levels > 1 kG accompanied by a significant loss of beam peripheral
layers, beam “braking” and preferential beam expansion along
the B-field lines. Cross B-field propagation of the PB in ambient plasma
did not differ substantially from the case without B-field, that is, no
deflection of the PB as a whole, which could be due to an insufficient
neutralization of the induced E-field inside the PB. Cross B-field
propagation of the IB in ambient plasma followed a single particle
trajectory deflection with a simultaneous significant loss of IB intensity
without any detectable bunching, indicating an adequate shorting of the
polarization E-field inside the IB.
Compression of a cylindrical hydrogen sample driven by an intense
co-axial heavy ion beam
Authors: TEMPORAL M. , CELA J. J. LOPEZ , PIRIZ A. R. , GRANDJOUAN N. , TAHIR N. A. , HOFFMANN D. H. H.
Published: April 2008

The compression of a cryogenic hydrogen cylindrical sample contained
in a hollow gold target driven by an intense co-axial uranium beam has
been studied. The ion distribution is assumed to be Gaussian in space and
parabolic in time. The hydrodynamics of the target is analyzed by means of
one- and two-dimensional numerical simulations. A parametric study is
performed to achieve the maximum average hydrogen density and temperature
as a function of the sample radius, total number of ions and spread of the
spatial ion distribution. A window in the beam-target parameters for which
hydrogen compression is higher than a factor of 10 and temperature is
below 0.2 eV has been found by considering a single bunch that contains 2
× 1011 uranium ions delivered in 100 ns. In this range of
high densities and low temperatures, it is expected that hydrogen may
become metallic.
Generation of picosecond high-density ion fluxes by skin-layer laser-plasma interaction
Authors: BADZIAK J. , GŁOWACZ S. , JABŁOŃSKI S. , PARYS P. , WOŁOWSKI J. , HORA H.
Published: April 2008

The possibilities of producing ultrahigh-current-density ps ion fluxes by the skin-layer interaction of a short (≤ 1ps) laser pulse with plasma were studied using two-fluid hydrodynamic simulations, and the time-of-flight measurements. Backward-emitted ion fluxes from a massive (Au) target as well as forward-emitted fluxes from various thin foil targets irradiated by a 1-ps laser pulse of intensity up to 2 × 1017W/cm2were recorded. Both the simulations and the measurements confirmed that using the short-pulse skin-layer interaction of a laser pulse with a thin pre-plasma layer in front of a solid target, a high-density collimated ion flux of extremely high ion current density (∼ 1010A/cm2close to the target), can be generated at laser intensity only ∼ 1017W/cm2. The ion current densities produced by this way were found to be comparable to (or even higher than) those estimated from recent short-pulse experiments using a target normal sheath acceleration mechanism at relativistic laser intensities. The effect of the target structure on the current densities and energies of forward-emitted ions is demonstrated.
Hydrodynamic instabilities in axisymmetric geometry self-similar
models and numerical simulations
Authors: BREIL J. , HALLO L. , MAIRE P.H. , OLAZABAL-LOUMÉ M.
Published: April 2008

Hydrodynamic instabilities play an important role in the target
compression for inertial confinement fusion (ICF). We present the
analytical solution of a perturbed isentropic implosion. We compare the
analytical solution to the results obtained with perturbation and
bi-dimensional Lagrangian hydrodynamic codes. We also compare results from
bi-dimensional code and perturbation code on an ICF like test case.
Ablation of metals with picosecond laser pulses: Evidence of long-lived non-equilibrium surface states
Authors: GAMALY E.G. , LUTHER-DAVIES B. , KOLEV V.Z. , MADSEN N.R. , DUERING M. , RODE A.V.
Published: April 2008

Experiments on laser ablation of metals in air, in vacuum, and in similar irradiation conditions, revealed that the ablation thresholds in air are up to three times lower than those measured in vacuum. Our analysis shows that this difference is caused by the existence of a long-lived transient non-equilibrium surface state at the solid-vacuum interface. The energy distribution of atoms at the surface is Maxwellian-like but with its high-energy tail truncated at the binding energy. We find that in vacuum the rate of energy transfer from the bulk to the surface layer to build the high-energy tail, which determines the lifetime of this non-equilibrium state, exceeds other characteristic timescales such as the surface cooling time. This prohibits thermal evaporation in vacuum for which the high-energy tail is essential. In air, however, collisions between the gas atoms and the surface markedly reduce the lifetime of this non-equilibrium surface state allowing thermal evaporation to proceed before the surface cools. It was experimentally observed that the difference between the ablation depth in vacuum and that in air disappears at the laser fluencies 2–3 times in excess of the vacuum threshold value. The material removal at this level of the deposited energy density attains the features of the non-equilibrium ablation similar for both cases. We find, therefore, that the threshold in vacuum corresponds to non-equilibrium ablation during the pulse, while thermal evaporation after the pulse is responsible for the lower ablation threshold observed in air. This paper provides direct experimental evidence of how the transient surface effects may strongly affect the onset and rate of a solid-gas phase transition.
Improved equation of state of metals in the liquid-vapor
region
Authors: RAY A. , SRIVASTAVA M.K. , KONDAYYA G. , MENON S.V.G.
Published: April 2008

The existing “quotidian equation state” model, based on
Thomas-Fermi theory, is modified so as to improve the low density region
of phase diagram of metals. A scheme for estimating the critical
parameters of liquid-vapor phase transition is proposed. The new model
reproduces experimental critical isotherms to a good degree of accuracy.
Furthermore, the proposed model is validated with thermodynamic data in
the liquid-vapor co-existence region, including results on isobaric
expansion as well as released isentropes.