Energy losses of solar cosmic rays in interplanetary space     

I. D. Palmer 《Solar physics》1973,30(1):235-242

A simple model of solar cosmic ray propagation which includes diffusion, convection, and energy loss by adiabatic deceleration is studied. A Monte Carlo technique is employed to investigate the variation of mean particle energy in the interplanetary medium after the impulsive release of mono-energetic particles at the Sun. At 1 AU typical energy losses are 43% at 20 h and 64% at 60 h after particle release for a diffusion coefficient (r)= ₀r with =+1/2 and ₀=1.33 × 10²¹ cm² s^–1. When ₀ in this model is reduced by a factor of 4, the energy loss is greater by a factor of 2 at 60 h after particle release. When is increased, the energy losses are greater. Using the model parameters above, an increase in solar wind speed from 300 to 600 km s^–-1 gives rise to energy losses that are greater again by factor of 2 at a time of 60 h. Results are compared with an observation by Murray et al. (1971) of a knee in the energy spectrum of solar protons. It is not considered likely that the change in the energy of the knee with time requires, in addition to adiabatic deceleration, another energy change process which acts to increase the energy of particles.Part of this work was performed while the author was at CSIRO, Division of Radiophysics, Epping, NSW, Australia; also supported in part by the U.S. Atomic Energy Commission.  相似文献   

Simple derivation of Symplectic Integrators with First Order Correctors     

Seppo Mikkola  Phil Palmer 《Celestial Mechanics and Dynamical Astronomy》2000,77(4):305-317

In this paper we consider almost integrable systems for which we show that there is a direct connection between symplectic methods and conventional numerical integration schemes. This enables us to construct several symplectic schemes of varying order. We further show that the symplectic correctors, which formally remove all errors of first order in the perturbation, are directly related to the Euler—McLaurin summation formula. Thus we can construct correctors for these higher order symplectic schemes. Using this formalism we derive the Wisdom—Holman midpoint scheme with corrector and correctors for higher order schemes. We then show that for the same amount of computation we can devise a scheme which is of order O(h ⁶)+(² h ²), where is the order of perturbation and h the stepsize. Inclusion of a modified potential further reduces the error to O(h ⁶)+(² h ⁴).This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

Dating ancient wood by high-sensitivity liquid scintillation counting and accelerator mass spectrometry—Pushing the boundaries     

Alan G. Hogg  L. Keith Fifield  Chris S.M. Turney  Jonathan G. Palmer  Rex Galbraith  Mike G.K. Baillie 《Quaternary Geochronology》2006,1(4):241-248

It is critical that a comprehensive terrestrial radiocarbon (¹⁴C) calibration curve is developed beyond 26 ka for high-precision calibration and correlation of climatic, environmental and archaeological records. Abundant sub-fossil New Zealand kauri (Agathis australis) wood, preserved in Oxygen Isotope Stage-2 and 3 peat swamps, provides an important resource for ¹⁴C calibration; nowhere else in the world does such an extensive collection of ancient wood exist. Although finite ¹⁴C ages beyond 50 ka are becoming routinely reported, few attempts have been made to demonstrate their accuracy or precision. Finite ages beyond 50 ka require optimization of all elements involved in sample preparation and ¹⁴C analysis. Here we discuss the methodology employed for optimizing the ¹⁴C dating of near-background wood samples by both benzene synthesis for liquid scintillation counting (LSC) or graphite synthesis for accelerator mass spectrometry (AMS). We report the mean background blank activities for both methods and present a statistical model for assigning blank standard errors when blank activity variation is over and above counting statistics. We also present duplicate analyses (using LSC and AMS) of nine successive samples of wood obtained from a sub-fossil kauri log near-background in age to investigate the significance of the measured blank levels and variability.  相似文献   

Comment on: “The dissolution rates of gibbsite in the presence of chloride, nitrate, silica, sulfate and citrate in open and closed systems at 20 °C” by M. Dietzel and G. Böhme     

David J. Wesolowski  Donald A. Palmer 《Geochimica et cosmochimica acta》2006,70(8):2140-2142

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Sea-level pressure variability around Antarctica since A.D. 1750 inferred from subantarctic tree-ring records     

R. Villalba  E. R. Cook  R. D. D’Arrigo  G. C. Jacoby  P. D. Jones  M. J. Salinger  J. Palmer 《Climate Dynamics》1997,13(6):375-390

 A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term climatic variability at higher latitudes in the Southern Hemisphere. Fifty long (1911–1985), homogeneous records of monthly mean sea-level pressure (MSLP) from the southern latitudes (15–65^°S) were intercorrelated on a seasonal basis to establish the most consistent, long-term Trans-Polar teleconnections during this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern Ocean are significantly correlated in a negative sense (r=−0.53, P<0.001). Climatically sensitive chronologies from Tierra del Fuego (54–55^°) and New Zealand (39–47^°) were used to develop verifiable reconstructions of summer (November to February) MSLP for both sectors of the Southern Ocean. These reconstructions, which explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse trends in MSLP from diametrically opposite sides of Antarctica have prevailed during the past two centuries. However, the strength of this relationship varies over time. Differences in normalized MSLP between the New Zealand and the South America-Antarctic Peninsula sectors were used to develop a Summer Trans-Polar Index (STPI), which represents an index of sea-level pressure wavenumber one in the Southern Hemisphere higher latitudes. Tree-ring based reconstructions of STPI show significant differences in large-scale atmospheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the New Zealand sector during the 1800s. In contrast, cyclonic activity appears to have been stronger in the mid-twentieth than previously for the South American sector of the Southern Ocean. Recent variations in MSLP in both regions are seen as part of the long-term dynamics of the atmosphere connecting opposite sides of Antarctica. A detailed analysis of the MSLP and STPI reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3.3–3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Oscillation Index suggests that teleconnections between the tropical ocean and extra-tropical MSLP variations may be influencing climate fluctuations at southern latitudes. Received: 18 December 1996/Accepted: 10 January 1997  相似文献   

Solid-solution aqueous-solution reactions between jarosite (KFe₃(SO₄)₂(OH)₆) and its chromate analog   总被引：1，自引：0，他引：1  

Dirk Baron  Carl D. Palmer 《Geochimica et cosmochimica acta》2002,66(16):2841-2853

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Nation building and resource management: The politics of ‘nature’ in Timor Leste     

Lisa Palmer  Demetrio do Amaral de Carvalho 《Geoforum》2008,39(3):1321-1332

This paper examines the role of custom and tradition in the process of nation building and resource management in post-independence Timor Leste (East Timor). While customary land tenure is alluded to but not explicitly recognized under the Timorese Constitution, it is clearly stated that all natural resources are owned by the State. However, this paper argues that rather than waiting for the government to create land and resource management related laws, local people in Timor Leste are making and remaking their own laws, mobilizing their customary practices and, increasingly, ‘performing’ their traditions in public demonstrations of their extant capacities. In part, this process can be read as a way of enticing in outsiders, making them a party to the law making process, a witness to its legitimacy. Often critical to such processes, is the ability of local level leaders to draw in outsiders through their engagements with the idea of ‘nature’ – a concept which allows diverse interests to come together in conversation and build relationships despite what is often a dissonance in the meanings and priorities attributed to the concept (see Tsing, A.L., 2005. Friction: An Ethnography of Global Connection. Princeton University Press, Princeton and Oxford). The paper focuses on a view from the margins – Tutuala in the far east of the country – and ways in which this community is attempting to both resist and embrace the developmental hegemony of a centrist state. This, it is argued, is a case which demonstrates the power of the local (both ritually and politically) to shape and intervene in the national development process and the associated discourses of nature preservation.  相似文献   

Incorporation of inorganic carbon by Antarctic cryptoendolithic fungi     

Palmer RJ  Friedmann EI 《Polarforschung》1988,58(2-3):189-191

Fungi isolated from the cryptoendolithic community of the Ross Desert are capable of fixing inorganic carbon. Results suggest that lichen mycobionts and parasymbionts are adapted to different water regimes in the cryptoendolithic environment.  相似文献   

Phase transitions in leucite: Dielectric properties and transition mechanism     

David C. Palmer  Ekhard K. H. Salje 《Physics and Chemistry of Minerals》1990,17(5):444-452

To investigate the mechanisms for the cubic-tetragonal phase transition in leucite (KAlSi₂O₆), the frequency dependence of the dielectric constant (), and of the electric conductivity (), have been measured as a function of temperature. The dielectric loss function, tan , contains two main features: (i) a classical Debye peak, with activation energy of 0.77 eV, ascribed to hopping of K-atoms between their channel (W) sites, via the vacant side-channel (S) sites; (ii) a heavily-overdamped relaxational mode which softens when the crystal is cooled towards the phase transition temperature. The latter relaxational mode shows a critical behaviour, and is thus directly correlated with the transition mechanism. As it is only the potassium ions that could relax at frequencies well below the optical phonon branches, it appears that their movement is relaxational (i.e. heavily overdamped) rather than phonon-like. At temperatures above the transition point, the relaxation of K⁺ in an electric field is analysed in terms of collective motions within tetragonal domains. Direct evidence for the existence of such domains follows from the presence of diffuse intensity in single-crystal X-ray diffraction experiments.  相似文献   

Morphology and tectonics of the Australian-Antarctic Discordance between 123° E and 128° E     

Jeb Palmer  Jean-Christophe Sempéré  David M. Christie  Jason Phipps Morgan 《Marine Geophysical Researches》1993,15(2):121-152

The Australian-Antarctic Discordance (AAD) is an anomalously deep and rugged zone of the Southeast Indian Ridge (SEIR) between 120° E and 128° E. The AAD contains the boundary between the Indian Ocean and Pacific Ocean isotopic provinces. We have analyzed SeaMarc II bathymetric and sidescan sonar data along the SEIR between 123° E and 128° E. The spreading center in the AAD, previously known to be divided into several transform-bounded sections, is further segmented by nontransform discontinuities which separate distinct spreading cells. Near the transform which bounds the AAD to the east, there is a marked change in the morphology of the spreading center, as well as in virtually every measured geochemical parameter. The spreading axis within the Discordance lies in a prominent rift valley similar to that observed along the Mid-Atlantic Ridge, although the full spreading rate within the AAD is somewhat faster than that of slow-spreading centers (~ 74 mm a^–1 vs. 0–40 mm a^–1). The AAD rift valleys show a marked contrast with the axial high that characterizes the SEIR east of the AAD. This change in axial morphology is coincident with a large (~ 1 km) deepening of the spreading axis. The segmentation characteristics of the AAD are analogous to those of the slow-spreading Mid-Atlantic Ridge, as opposed to the SEIR east of the AAD, which exhibits segmentation characteristics typical of fast-spreading centers. Thus, the spreading center within and east of the AAD contains much of the range of global variability in accretionary processes, yet it is a region free from spreading rate variations and the volumetric and chemical influences of hotspots. We suggest that the axial morphology and segmentation characteristics of the AAD spreading centers are the result of the presence of cooler than normal mantle. The presence of a cool mantle and the subsequent diminution of magma supply at a constant spreading rate may engender the creation of anomalously thick brittle lithosphere within the AAD, a condition which favor, the creation of an axial rift valley and of thin oceanic crust, in agreement with petrologic studies. The morphologies of transform and non-transform discontinuities within the Discordance also possess characteristics consistent with the creation of anomalously thick lithosphere in the region. The upper mantle viscosity structure which results from lower mantle temperatures and melt production rates may account for the similarity in segmentation characteristics between the AAD and slow-spreading centers. The section of the AAD which overlies the isotopic boundary is associated with chaotic seafloor which may be caused by an erratic pattern of magmatism and/or complex deformation associated with mantle convergence. Finally, the pattern of abyssal hill terrain within a portion of the AAD supports previous models for the formation of abyssal hills at intermediate- and slow-spreading ridges, and provides insights into how asymmetric spreading is achieved in this region.  相似文献