Bounce-free spherical hydrodynamic implosion

In a bounce-free spherical hydrodynamic implosion, the post-stagnation hot core plasma does not expand against the imploding flow. Such an implosion scheme has the advantage of improving the dwell time of the burning fuel, resulting in a higher fusion burn-up fraction. The existence of bounce-free spherical implosions is demonstrated by explicitly constructing a family of self-similar solutions to the spherically symmetric ideal hydrodynamic equations. When applied to a specific example of plasma liner driven magneto-inertial fusion, the bounce-free solution is found to produce at least a factor of four improvement in dwell time and fusion energy gain.Comment: accepted by Phys. Plasmas (Nov. 7, 2011); for Ref. 11, please see ftp://ftp.lanl.gov/public/kagan/liner_evolution.gi

Insights from 20 years of temperature parallel measurements in Mauritius around the turn of the 20th century

There is considerable import in creating more complete, better understood holdings of early meteorological data. Such data permit an improved understanding of climate variability and long-term changes. Early records are particularly incomplete in the tropics, with implications for estimates of global and regional temperature. There is also a relatively low level of scientific understanding of how these early measurements were made and, as a result, of their homogeneity and comparability to more modern techniques and measurements. Herein we describe and analyse a newly rescued set of long-term, up to six-way parallel measurements undertaken over 1884–1903 in Mauritius, an island situated in the southern Indian Ocean. Data include (i) measurements from a well-ventilated room, (ii) a shaded thermograph, (iii) instruments housed in a manner broadly equivalent to a modern Stevenson screen, (iv) a set of measurements by a hygrometer mounted in a Stevenson screen, and for a much shorter period (v) two additional Stevenson screen configurations. All measurements were undertaken within an ∼ 80 m radius of each other. To our knowledge this is the first such multidecadal multi-instrument assessment of meteorological instrument transition impacts ever undertaken, providing potentially unique insights. The intercomparison also considers the impact of different ways of deriving daily and monthly averages. The long-term comparison is sufficient to robustly characterize systematic offsets between all the instruments and seasonally varying impacts. Differences between all techniques range from tenths of a degree Celsius to more than 1 ∘C and are considerably larger for maximum and minimum temperatures than for means or averages. Systematic differences of several tenths of a degree Celsius also exist for the different ways of deriving average and mean temperatures. All differences, except two average temperature series pairs, are significant at the 0.01 level using a paired t test. Given that all thermometers were regularly calibrated against a primary Kew standard thermometer maintained by the observatory, this analysis highlights significant impacts of instrument exposure, housing, siting, and measurement practices in early meteorological records. These results reaffirm the importance of thoroughly assessing the homogeneity of early meteorological records

Insights from 20 years of temperature parallel measurements in Mauritius around the turn of the 20th century

There is considerable import in creating more complete, better understood holdings of early meteorolog- ical data. Such data permit an improved understanding of climate variability and long-term changes. Early records are particularly incomplete in the tropics, with implications for estimates of global and regional temperature. There is also a relatively low level of scientific understanding of how these early measurements were made and, as a result, of their ho- mogeneity and comparability to more modern techniques and measurements. Herein we describe and analyse a newly rescued set of long-term, up to six-way parallel measure- ments undertaken over 1884–1903 in Mauritius, an island situated in the southern Indian Ocean. Data include (i) mea- surements from a well-ventilated room, (ii) a shaded thermo- graph, (iii) instruments housed in a manner broadly equiv- alent to a modern Stevenson screen, (iv) a set of measure- ments by a hygrometer mounted in a Stevenson screen, and for a much shorter period (v) two additional Stevenson screen configurations. All measurements were undertaken within an ∼ 80 m radius of each other. To our knowledge this is the first such multidecadal multi-instrument assessment of meteoro- logical instrument transition impacts ever undertaken, pro- viding potentially unique insights. The intercomparison also considers the impact of different ways of deriving daily and monthly averages. The long-term comparison is sufficient to robustly characterize systematic offsets between all the in- struments and seasonally varying impacts. Differences be- tween all techniques range from tenths of a degree Celsius to more than 1 ◦C and are considerably larger for maximum and minimum temperatures than for means or averages. System- atic differences of several tenths of a degree Celsius also exist for the different ways of deriving average and mean tempera- tures. All differences, except two average temperature series pairs, are significant at the 0.01 level using a paired t test. Given that all thermometers were regularly calibrated against a primary Kew standard thermometer maintained by the ob- servatory, this analysis highlights significant impacts of in- strument exposure, housing, siting, and measurement prac- tices in early meteorological records. These results reaffirm the importance of thoroughly assessing the homogeneity of early meteorological records

An integrative geochronological framework for the pleistocene So'a basin (Flores, Indonesia), and its implications for faunal turnover and hominin arrival

Flores represents a unique insular environment with an extensive record of Pleistocene fossil remains and stone artefacts. In the So\u27a Basin of central Flores these include endemic Stegodon, Komodo dragons, giant tortoises, rats, birds and hominins, and lithic artefacts that can be traced back to at least one million years ago (1 Ma). This comprehensive review presents important new data regarding the dating and faunal sequence of the So\u27a Basin, including the site of Mata Menge where Homo floresiensis-like fossils dating to approximately 0.7 Ma were discovered in 2014. By chemical fingerprinting key silicic tephra originating from local and distal eruptive sources we have now established basin-wide tephrostratigraphic correlations, and, together with new numerical ages, present an update of the chronostratigraphy of the So\u27a Basin, with major implications for the faunal sequence. These results show that a giant tortoise and the diminutive proboscidean Stegodon sondaari last occurred at the site of Tangi Talo ∼1.3 Ma, and not 0.9 Ma as previously thought. We also present new data suggesting that the disappearance of giant tortoise and S. sondaari from the sedimentary record occurred before, and/or was coincident with, the earliest hominin arrival, as evidenced by the first records of lithic artefacts occurring directly below the 1 Ma Wolo Sege Tephra. Artefacts become common in the younger layers, associated with a distinct fauna characterized by the medium-sized Stegodon florensis and giant rat Hooijeromys nusatenggara. Furthermore, we describe a newly discovered terrace fill, which extends the faunal record of Stegodon in the So\u27a Basin to the Late Pleistocene. Our evidence also suggests that the paleoenvironment of the So\u27a Basin became drier around the time of the observed faunal transition and arrival of hominins on the island, which could be related to an astronomically-forced climate response at the onset of the Mid-Pleistocene Transition (MPT; ∼1.25 Ma) leading to increased aridity and monsoonal intensity

Experimental Investigation of the Properties and Phase State of Thick Aluminum Surfaces Pulsed to Megagauss Level Magnetic Field in a Z-Pinch Geometry

Thermal transformation to plasma of an aluminum surface pulsed to multi-megagauss magnetic field is observed to occur when the surface field reaches a threshold level of 2.2 MG. Magnetic field is pulsed on the surface of cylindrical metallic rods. Rods are thick, with radii exceeding the magnetic field penetration depth. Ohmic heating is confined to a skin layer, with the magnetic field penetration depth determined by diffusion and hydrodynamic processes. Initial rod diameters ranging from 2.00 to 0.50 mm are pulsed with 1.0 MA peak current by the Zebra z-pinch. Due to the high transmission line impedance (1.9 ohm) of Zebra, the current waveform is insensitive to the initial rod diameter. The Zebra current consistently rises exponentially to 100 kA (with rise time, tau=13 ns), and then linearly from 100 to 900 kA for 70 ns to a maximum current of 1.0 MA. By altering the initial rod diameter, a variety of magnetic field and current density profiles are examined. For initial rod diameters of 2.00 and 0.50 mm, magnetic field rise rates vary from 30 and 80 MG/microsecond, and peak surface fields reach 1.5 and 4 MG, respectively. Novel contact configurations and load surface profiles mitigate plasma formation from contact arcing or electric-field-driven electron avalanche, ensuring that plasma forms thermally, as a result of ohmic or compression heating.Aluminum plasma is observed through a variety of independently measured phenomena. First, for rod surfaces pulsed above the magnetic field threshold of 2.2 MG, multi eV brightness temperatures are observed, clearly indicating plasma for aluminum. For example, peak brightness temperatures reach 20 and 36 eV for 1.00 and 0.50 mm rods, respectively. Plasma forms at lower current and reaches higher temperatures as the intial rod diameter is decreased. Second, aluminum ion species are distinguished via extreme ultraviolet (EUV) spectroscopy. Line spectra from Al-3-plus and Al-4-plus ions are obtained. The average ion charge and line ratios depend strongly upon temperature, and taking the ratio of line intensities results in an estimated peak plasma temperature of 15 eV for 1.00-mm-diameter rods. Third, EUV photon flux consistent with multi-eV temperature is recorded by Al or Si/Zr filtered photodiodes sensitive to photon energies from 16 to 73 eV, or 60 to 100 eV, respectively. Fourth, magnetohydrodynamic (MHD) instabilities form. Instability development depends on the conductivity of the low density expanding surface material. High resistivity vapor interacts weakly with magnetic field; therefore, flute instabilities are attributed to surface plasma. For those rods which do not reach the 2.2 MG magnetic field threshold, no evidence of surface plasma is obtained. For 2.00-mm-diameter rods, which reach peak surface field of only 1.7 MG, surface temperatures remain cool (peak brightness temperatures reach 0.7 eV), no EUV emission can be measured, and even while carrying 1.0 MA of current, and after significant radial expansion, no surface instability is observed. The experiment offers the first detailed study of plasma formation by pulsed magnetic field on a thick metallic surface carrying a skin current. The magnetic field threshold for plasma formation, surface brightness temperature, radial expansion velocity, instability growth, and ionization state have been measured. The effects of hardware design, load geometry, Al alloy, and surface smoothness have been carefully examined, creating a dataset that can be used for the design of practical systems. The experiment has achieved thermal, uniform, and symmetric plasma formation, providing a meaningful comparison for MHD simulations

Craniofacial morphology of 'Homo floresiensis': Description, taxonomic affinities, and evolutionary implication

This paper describes in detail the external morphology of LB1/1, the nearly complete and only known cranium of 'Homo floresiensis'. Comparisons were made with a large sample of early groups of the genus 'Homo' to assess primitive, derived, and unique craniofacial traits of LB1 and discuss its evolution. Principal cranial shape differences between 'H. floresiensis' and 'Homo sapiens' are also explored metrically. The LB1 specimen exhibits a marked reductive trend in its facial skeleton, which is comparable to the 'H. sapiens' condition and is probably associated with reduced masticatory stresses. However, LB1 is craniometrically different from 'H. sapiens' showing an extremely small overall cranial size, and the combination of a primitive low and anteriorly narrow vault shape, a relatively prognathic face, a rounded oval foramen that is greatly separated anteriorly from the carotid canal/jugular foramen, and a unique, tall orbital shape. Whereas the neurocranium of LB1 is as small as that of some 'Homo habilis' specimens, it exhibits laterally expanded parietals, a weak suprameatal crest, a moderately flexed occipital, a marked facial reduction, and many other derived features that characterize post-'habilis Homo'. Other craniofacial characteristics of LB1 include, for example, a relatively narrow frontal squama with flattened right and left sides, a marked frontal keel, posteriorly divergent temporal lines, a posteriorly flexed anteromedial corner of the mandibular fossa, a bulbous lateral end of the supraorbital torus, and a forward protruding maxillary body with a distinct infraorbital sulcus. LB1 is most similar to early Javanese 'Homo erectus' from Sangiran and Trinil in these and other aspects. We conclude that the craniofacial morphology of LB1 is consistent with the hypothesis that 'H. floresiensis' evolved from early Javanese 'H. erectu's with dramatic island dwarfism. However, further field discoveries of early hominin skeletal remains from Flores and detailed analyses of the finds are needed to understand the evolutionary history of this endemic hominin species

Craniofacial morphology of Homo floresiensis: description, taxonomic affinities, and evolutionary implication

This paper describes in detail the external morphology of LB1/1, the nearly complete and only known cranium of Homo floresiensis. Comparisons were made with a large sample of early groups of the genus Homo to assess primitive, derived, and unique craniofacial traits of LB1 and discuss its evolution. Principal cranial shape differences between H. floresiensis and Homo sapiens are also explored metrically. The LB1 specimen exhibits a marked reductive trend in its facial skeleton, which is comparable to the H. sapiens condition and is probably associated with reduced masticatory stresses. However, LB1 is craniometrically different from H. sapiens showing an extremely small overall cranial size, and the combination of a primitive low and anteriorly narrow vault shape, a relatively prognathic face, a rounded oval foramen that is greatly separated anteriorly from the carotid canal/jugular foramen, and a unique, tall orbital shape. Whereas the neurocranium of LB1 is as small as that of some Homo habilis specimens, it exhibits laterally expanded parietals, a weak suprameatal crest, a moderately flexed occipital, a marked facial reduction, and many other derived features that characterize post- habilis Homo. Other craniofacial characteristics of LB1 include, for example, a relatively narrow frontal squama with flattened right and left sides, a marked frontal keel, posteriorly divergent temporal lines, a posteriorly flexed anteromedial corner of the mandibular fossa, a bulbous lateral end of the supraorbital torus, and a forward protruding maxillary body with a distinct infraorbital sulcus. LB1 is most similar to early Javanese Homo erectus from Sangiran and Trinil in these and other aspects. We conclude that the craniofacial morphology of LB1 is consistent with the hypothesis that H. floresiensis evolved from early Javanese H. erectus with dramatic island dwarfism. However, further field discoveries of early hominin skeletal remains from Flores and detailed analyses of the finds are needed to understand the evolutionary history of this endemic hominin species. Copyright 2011 Elsevier Ltd

Insights from 20 years of temperature parallel measurements in Mauritius around the turn of the 20th century

There is considerable import in creating more complete, better understood holdings of early meteorolog- ical data. Such data permit an improved understanding of climate variability and long-term changes. Early records are particularly incomplete in the tropics, with implications for estimates of global and regional temperature. There is also a relatively low level of scientific understanding of how these early measurements were made and, as a result, of their ho- mogeneity and comparability to more modern techniques and measurements. Herein we describe and analyse a newly rescued set of long-term, up to six-way parallel measure- ments undertaken over 1884–1903 in Mauritius, an island situated in the southern Indian Ocean. Data include (i) mea- surements from a well-ventilated room, (ii) a shaded thermo- graph, (iii) instruments housed in a manner broadly equiv- alent to a modern Stevenson screen, (iv) a set of measure- ments by a hygrometer mounted in a Stevenson screen, and for a much shorter period (v) two additional Stevenson screen configurations. All measurements were undertaken within an ∼ 80 m radius of each other. To our knowledge this is the first such multidecadal multi-instrument assessment of meteoro- logical instrument transition impacts ever undertaken, pro- viding potentially unique insights. The intercomparison also considers the impact of different ways of deriving daily and monthly averages. The long-term comparison is sufficient to robustly characterize systematic offsets between all the in- struments and seasonally varying impacts. Differences be- tween all techniques range from tenths of a degree Celsius to more than 1 ◦C and are considerably larger for maximum and minimum temperatures than for means or averages. System- atic differences of several tenths of a degree Celsius also exist for the different ways of deriving average and mean tempera- tures. All differences, except two average temperature series pairs, are significant at the 0.01 level using a paired t test. Given that all thermometers were regularly calibrated against a primary Kew standard thermometer maintained by the ob- servatory, this analysis highlights significant impacts of in- strument exposure, housing, siting, and measurement prac- tices in early meteorological records. These results reaffirm the importance of thoroughly assessing the homogeneity of early meteorological records