Non-local diffusion and the chemical structure of molecular clouds

Observations of fluctuations in the redshifted 21-cm radiation from neutral hydrogen (H  i ) are perceived to be an important future probe of the universe at high redshifts. Under the assumption that at redshifts   z ≤ 6  (post-reionization era) the H  i traces the underlying dark matter with a possible bias, we investigate the possibility of using observations of redshifted 21-cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expected signal is ∼ 0.1  mJy at  325  MHz ( z = 3.4)  for the small baselines at the Giant Metrewave Radio Telescope, the strength being a few times larger at higher frequencies  (610 MHz, z = 1.3)  . Further, the magnitude of the signal from the bispectrum is predicted to be comparable to that from the power spectrum, allowing a detection of both in roughly the same integration time. The H  i signal is found to be uncorrelated beyond frequency separations of ∼1.3 MHz whereas the continuum sources of contamination are expected to be correlated across much larger frequencies. This signature can in principle be used to distinguish the H  i signal from the contamination. We also consider the possibility of using observations of the bispectrum to determine the linear and quadratic bias parameters of the H  i at high redshifts, this having possible implications for theories of galaxy formation.     

Stratigraphy of total metals in PIRLA sediment cores

Sediment cores from 30 low-alkalinity lakes in northern New England (NE), New York (NY), the northern Great Lakes States (NGLS) of Minnesota, Michigan, and Wisconsin, and Florida (FL) have been dated by ²¹⁰Pb and analyzed for water and organic content, eight major elements (Al, Ti, Fe, Mn, Ca, Mg, Na, K) plus four trace metals (Pb, Zn, Cu, and V). Variations in the percentages of major elements through time are dominated by long-term independent variations in the abundance of SiO₂, FeO, and to a lesser extent Ca and Al. Additional variations are caused by varying proportions of inorganic matter. Major variations in chemistry are generally unrelated to documented distrubances in the watersheds; most disturbances are minor fires or selective logging.Accelerated accumulation of Pb from atmospheric sources into sediment first occurs in sediment dated between 1800 and 1850 in NY and NE, slightly later in the NGLS region, and about 1900 in FL. Modern accumulation rates in all areas are comparable (ca. 1 to 4 g cm^–2 yr^–1). Accumulation rates of Pb in some lakes have declined significantly from 1975 to 1985. Atmospheric deposition of anthropogenic Zn and Cu is also indicated by generally increasing accumulation rates in sediment cores, but the record is not as clear nor are chemical profiles in all lakes parallel to the trends in atmospheric emissions inferred on the basis of fossil fuel consumption, smelting, and other industrial activities. Inter-lake variations in profiles of Cu and Zn are large. Vanadium accumulation rates increase by the 1940s in NY and NE, but not until the 1950s in the NGLS region. This timing correlates with regional trends in the combustion of fuel oil, a major source of atmospheric V.Acidification of some of the lakes is suggested by decreases in the concentration and accumulation rates of Mn, Ca, and Zn in recent sediment, relative to other elements of catchment origin. The decreases generally occur slightly before the onset of acidification as indicated by diatoms. Increased sediment accumulation rates for Fe may indicate the acidification of watershed soils. The use of the accumulation rate of TiO₂ as an indicator of rates of erosion and for normalization of trace metal accumulation rates is in question for lakes where the flux of TiO₂ from the atmosphere varies and is a significant fraction of the total flux of TiO₂ to the sediment.This is the thirteenth of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.     

Formation of ‘Beach Rock’ at Siesta Key, Florida and its influence on barrier island development

Seaward-dipping strata of carbonate-cemented shell debris located along the coast of Siesta Key on the Gulf Coast of the Florida peninsula have long been interpreted to be beachrock equivalent in age to the Pleistocene Anastasia Formation (Stage 5e) of the east coast of Florida. Detailed examination of thin sections along with radiometric dating and isotopic analyses demonstrates clearly that this is a Holocene deposit that is not beachrock but was lithified in a meteoric environment. Whole rock dates, dates from shells only, and from cement only demonstrate that these beach deposits were in place by at least 1800 yr BP and might have been there as long ago as 4300 yr BP. This means that some type of barrier island was in place at that time. Previous investigations have depicted Siesta Key as having a maximum age of 3000 yr with these deposits being located about 2 km landward of the beach deposits. This suggests that the beach deposits might have been the site of the original position of Siesta Key. These data also indicate that sea level must have been near its present position at the time that these foreshore beach deposits were deposited; sometime between 1800 and 4300 yr ago. This scenario indicates that sea level along this coastal reach probably reached its present level at least about 2000 yr ago.     

The Tully–Fisher relation for S0 galaxies

We present a study of the local B - and K _s-band Tully–Fisher relation (TFR) between absolute magnitude and maximum circular speed in S0 galaxies. To make this study, we have combined kinematic data, including a new high-quality spectral data set from the Fornax cluster, with homogeneous photometry from the Third Reference Catalogue of Bright Galaxies and Two Micron All Sky Survey catalogues, to construct the largest sample of S0 galaxies ever used in a study of the TFR. Independent of environment, S0 galaxies are found to lie systematically below the TFR for nearby spirals in both optical and infrared bands. This offset can be crudely interpreted as arising from the luminosity evolution of spiral galaxies that have faded since ceasing star formation.
However, we also find a large scatter in the TFR. We show that most of this scatter is intrinsic, not due to the observational uncertainties. The presence of such a large scatter means that the population of S0 galaxies cannot have formed exclusively by the above simple fading mechanism after all transforming at a single epoch. To better understand the complexity of the transformation mechanism, we have searched for correlations between the offset from the TFR and other properties of the galaxies such as their structural properties, central velocity dispersions and ages (as estimated from line indices). For the Fornax cluster data, the offset from the TFR correlates with the estimated age of the stars in the individual galaxies, in the sense and of the magnitude expected if S0 galaxies had passively faded since being converted from spirals. This correlation implies that a significant part of the scatter in the TFR arises from the different times at which galaxies began their transformation.     

Sea-level and subsidence data from a Late Holocene back-barrier lagoon (Valle Standiana, Ravenna, Italy)

Late Holocene back-barrier sediments have been studied in a former lagoon reclaimed during the last century. Several shallow boreholes were cored, from which nine organic-rich samples were selected for radiocarbon dating, and others for palynological and palaeontological analysis. This enabled the reconstruction of the evolution of a back-barrier coastal basin during the late Holocene coastline progradation. Since late Roman times, the rate of relative sea-level rise (RSLR) has increased from 1.1 mm/yr to over 2 mm/yr, even after removal of the main human impacts during of the last century. This change is ascribed to sediment compaction related to changes in the hydrological regime, and possibly to an isostatic subsidence wave accompanying the northward shift of the Po Delta during the last 2000 years.     

Diurnal surface temperature difference index derived from ground-based meteorological measurements for assessment of moisture availability

Droughts have become widespread in the Northern Hemisphere, including in China, where they have affected farmland resources on the Loess Plateau. Given this background, we proposed a new index, the Normalized Day-Night Surface Temperature Index (NTDI), to estimate moisture availability (m_a), defined as the ratio of actual to reference evapotranspiration. The NTDI is defined as the ratio of the difference between the maximum daytime surface temperature and the minimum nighttime surface temperature, to the difference between the maximum and minimum surface temperatures estimated from meteorological data by applying energy balance equations.To calculate the index, we used data of 20 clear-sky meteorological observations made during the 2005 growing season at a natural grassland station in the Liudaogou River basin on the Loess Plateau. The NTDI showed a significant inverse exponential correlation with m_a (R² = 0.97, p < 0.001), whereas the numerator of the index (the maximum daytime surface temperature minus the minimum nighttime surface temperature) was only weakly correlated with m_a (R² = 0.24, p = 0.03). This result indicates that normalization relative to the index denominator (maximum surface temperature − minimum surface temperature) dramatically improved the accuracy of the estimate.     

Correlation Between the Sunspot Number,the Total Solar Irradiance,and the Terrestrial Insolation

Our study deals with the correlations between the solar activity on the one hand and the solar irradiance above the Earth’s atmosphere and at ground level on the other. We analyzed the combined ACRIM I+II time series of the total solar irradiance (TSI), the Mauna Loa time series of terrestrial insolation data, and data of terrestrial cosmic ray fluxes. We find that the correlation between the TSI and the sunspot number is strongly non-linear. We interpret this as the net balance between brightening by faculae and darkening by sunspots where faculae dominate at low activity and sunspots dominate at high activity. Such a behavior is hitherto known from stellar analogs of the Sun in a statistical manner. We perform the same analysis for the Mauna Loa data of terrestrial insolation. Here we find that the linear relation between sunspot number and insolation shows more than 1% rise in insolation by sunspot number variations which is much stronger than for the TSI. Our conclusion is that the Earth atmosphere acts as an amplifier between space and ground, and that the amplification is probably controlled by solar activity. We suspect the cosmic rays intensity as the link between solar activity and atmospheric transparency. A Fourier analysis of the time series of insolation shows three dominant peaks: 10.5, 20.4, and 14.0 years. As a matter of fact, the cosmic rays data show the same pattern of significant peaks: 10.7, 22.4, and 14.9 years. This analogy supports our idea that the cosmic rays variation has influence on the transparency of the Earth atmosphere.     

Three-Dimensional (3-D) Reconstructions of EISCAT IPS Velocity Data in the Declining Phase of Solar Cycle 23

The European Incoherent SCATter (EISCAT) radar has been used for remote-sensing observations of interplanetary scintillation (IPS) for a quarter of a century. During the April/May 2007 observing campaign, a large number of observations of IPS using EISCAT took place to give a reasonable spatial and temporal coverage of solar wind velocity structure throughout this time during the declining phase of Solar Cycle 23. Many co-rotating and transient features were observed during this period. Using the University of California, San Diego three-dimensional (3-D) time-dependent computer assisted tomography (C.A.T.) solar-wind reconstruction analysis, we show the velocity structure of the inner heliosphere in three dimensions throughout the time interval of 20 April through 20 May 2007. We also compare to white-light remote-sensing observations of an interplanetary coronal mass ejection (ICME) seen by the STEREO Ahead spacecraft inner Heliospheric Imager on 16 May 2007, as well as to in-situ solar-wind measurements taken with near-Earth spacebourne instrumentation throughout this interval. The reconstructions show clear co-rotating regions during this period, and the time-series extraction at spacecraft locations compares well with measurements made by the STEREO, Wind, and ACE spacecraft. This is the first time such clear structures have been revealed using this 3-D technique with EISCAT IPS data as input.     

Further investigations of the fog in the photo-electric condensation nucleus counter

Summary The effect on extinction of isothermal distillation, shrinking of the droplets by evaporation without recondensation of the liberated water vapour, coagulation and differential settling of the fog droplets which take place in the fog of a photo-electric nucleus counter and which can produce a small additional extinction («creep») in the first seconds after its formation, were numerically examined. The relative contribution of each process to the total creep observed is assessed. It is found that isothermal distillation can produce amounts of creep (up to 1.70%) which exceed considerably those caused by evaporation or coagulation. The results of these computations explain the occurrence of creep with concentrations greater than approx. 25 000 nuclei/cm³ in fog-tubes of 3.85 cm air-column diameter.That the disappearance of creep in fog-tubes of diameters 2.5 cm and less is due to the accelerated heat-flow from the walls of the narrow fog-tube was previously proved by reducing appropriately the diameter of the light pencil through the fog. In order to meet the objection that by restricting the cross section of the light pencil the fine structure of the fog comes into play, the increase in the travel time of the heat from the walls was achieved this time by using a photo-electric counter with a fog-tube of 8 cm diameter and a light beam of 2.8 cm diameter as in the «Standard Counter 1946». As expected, creep was found in every single measurement up to readings of 53%. Typical examples of the galvanometer pointer-movement and photographic records of the extinction during fog formation in such a wide fog-tube for readings between approx. 10 and 76% are given and their peculiarities discussed.The extinction over the range from 175 000 to 20 000 nuclei/cm³ was also measured with a red and a blue monochromatic interference filter and the results contrasted against the computed extinctions for these two wave lengths. It was ascertained that for the same number of nuclei the extinction for red light is in general larger than that for blue; the difference between the observed extinctions varies considerably, becoming zero or even negative. The most striking feature, however, is the different course of the extinction for the two wave lengths as a function of the number or size of the droplets.The size of the fog droplets in the counter was deduced from the extinction measurements for these two wave lengths and by collecting the falling droplets on coated slides. The radius of the droplets obtained by the optical method varies from 1.81 to 3.19 when the extinction decreases from 86 to 56%. The radius of the droplets as deduced from gelatine coated slides dyed with Naphtol Green B increases from 1.44 at 67.4% extinction (42 400 nuclei/cm³) to 6.30 at 15.6% (858 nuclei/cm³).

---

Zusammenfassung Der Einflus der isothermalen Destillation, des Einschrumpfens der Tröpfchen durch Verdunstung ohne Wiederkondensation des freiwerdenden Wasserdampfes, des Zusammenfliessens und Absetzens der Nebeltröpfchen auf die Extinktion, welche im Nebel des photo-elektrischen Kernzählers stattfinden und die in den ersten Sekunden nach seiner Bildung eine kleine zusätzliche Extinktion (im folgenden Kriechen genannt) erzeugen können, wurde numerisch geprüft. Der entsprechende Beitrag jedes einzelnen der oben genannten Prozesse zum Gesamtbetrag des beobachteten Kriechens wurde abgeschätzt. Es wurde gefunden, dass isothermale Destillation zusätzliche Extinktions-Beträge (bis zu 1.70%) erzeugen kann, welche jene durch Verdunstung oder Zusammenfliessen der Tröpfchen verursachten, beträchtlich übersteigen. Die Resultate dieser Berechnungen erklären das Auftreten des Kriechens bei Konzentrationen grösser als ca. 25 000 Kerne per cm³ in Nebelrohren von 3.85 cm Luftsäulen-Durchmesser.Dass das Verschwinden des Kriechens in Nebelrohren mit einem Durchmesser von 2.5 cm und weniger dem beschleunigten Wärmefluss von den Wänden des engen Nebelrohres zuzuschreiben ist, wurde früher durch eine entsprechende Verengung des Lichtbündels, welches zur Durchleuchtung des Nebels verwendet wird, bewiesen. Um dem Einwand zu begegnen, dass bei so starker Verkleinerung des Querschnittes des Lichtbündels, wie sie benützt wurde, schon die Feinstruktur des Nebels eine Rolle spielt, wurde diesmal die Verlängerung der Laufzeit der Wärme von den Wänden durch Erweiterung des Nebelrohres auf 8 cm Durchmesser erzielt, während der Durchmesser des Lichtbündels mit 2.8 cm — wie im «Standard photo-elektrischen Kernzähler 1946» — unverändert belassen wurde. Entsprechend den Erwartungen wurde bei jeder einzelnen Messung bis zu Lesungen von 53% Kriechen festgestellt. Typische Beispiele der Bewegung des Galvanometer-Zeigers und photographische Aufzeichnungen der Extinktion während der Nebelbildung in einem solchen weiten Nebelrohr werden für Lesungen zsischen ca. 10 und 76% gegeben und ihre Eigentümlichkeiten besprochen.Die Extinktion für Konzentrationen zwischen 175 000 und 20 000 Kernen per cm³ wurde auch mit einem roten und blauen Interferenz-Filter gemessen und die Resultate den für diese zwei Wellenlängen berechneten Extinktionen gegenübergestellt. Es wurde festgestellt, dass bei der gleichen Kernzahl die Extinktion für rotes Licht im allgemeinen grösser ist als jene für blaues; die Differenz zwischen den beobachteten Extinktionen schwankt beträchtlich, wird null oder sogar negativ. Am auffallendsten ist jedoch der verschiedene Verlauf der Extinktion für die zwei Wellenlängen als Funktion der Zahl oder Grösse der Tröpfchen.Die Grösse der Nebeltröpfchen im Nebelrohr des photo-elektrischen Kernzählers wurde aus den Extinktions-Messungen in diesen zwei Wellenlängen und durch Auffangen der fallenden Tröpfchen auf Mikroskop-Objektträgern und Deckgläsern, welche mit gefärbter Gelatine überzogen waren, bestimmt. Der Radius der Tröpfchen, welcher mittels der optischen Methode ermittelt wurde, liegt zwischen 1.81 und 3.19 , wenn die Extinktion von 86 auf 56% abnimmt.Der Tröpfchenradius, wie er aus den Flecken auf den Mikroskopgläschen, deren Gelatineüberzug mit Naphtol Grün B eingefärbt war, bestimmt wurde, wächst von 1.44 bei 67.4% Extinktion (42 400 Kerne per cm³) auf 6.30 bei 15.6% (858 Kerne per cm³).

---

---

The research reported in this article has been sponsored and supported in part by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, United States Air Force, under Contract AF 61(052)-26, through the European Office, ARDC in Brussels.