Continuum Lowering -- A New Perspective

What is meant by continuum lowering and ionization potential depression (IPD) in a Coulomb system depends upon precisely what question is being asked. It is shown that equilibrium (equation-of-state) phenomena and non-equilibrium dynamical processes like photoionization are characterised by different values of the IPD. In the former, the ionization potential of an atom embedded in matter is the difference in the free energy of the many-body system between states of thermodynamic equilibrium differing by the ionization state of just one atom. Typically, this energy is less than that required to ionize the same atom in vacuo. Probably, the best known example of such an IPD is that of Stewart and Pyatt (SP). However, it is a common misconception that this formula should apply directly to the energy of a photon causing photoionization, since this is a local adiabatic process that occurs in the absence of a response from the surrounding plasma. To achieve the prescribed final equilibrium state, additional energy, in the form of heat and work, is transferred between the atom and its surroundings. This additional relaxation energy is sufficient to explain the discrepancy between recent spectroscopic measurements of IPD in dense plasmas and the predictions of the SP formula. This paper provides a detailed account of an analytical approach to calculating thermodynamic and spectroscopic (adiabatic) IPDs in multicomponent Coulomb systems of arbitrary coupling strength. The ramifications are carefully examined in order to elucidate the roles of the various IPD forms. A formulation in terms of free energy leads to an analytical equation of state (EoS) that is thermodynamically self-consistent, provided that the bound and free electrons are dynamically separable. Of the various proposed formulae, the Spectroscopic (adiabatic) IPD gives the most consistent agreement with spectroscopic measurements.Comment: 80 pages 3 figures. S1. Expanded intro incl: summary of experiments; outline of ionization process & basis of local non-equilibrium hypothesis; revised para on connection with microfield. S2. New para on connection with self-energy; outline of basic continuum-lowering model used to illustrate the new ideas. S3. Rearranged text. S6. Revised & retitled. References: expanded. Minor changes throughou

Extractable nitrogen and microbial community structure respond to grassland restoration regardless of historical context and soil composition.

Grasslands have a long history of invasion by exotic annuals, which may alter microbial communities and nutrient cycling through changes in litter quality and biomass turnover rates. We compared plant community composition, soil chemical and microbial community composition, potential soil respiration and nitrogen (N) turnover rates between invaded and restored plots in inland and coastal grasslands. Restoration increased microbial biomass and fungal : bacterial (F : B) ratios, but sampling season had a greater influence on the F : B ratio than did restoration. Microbial community composition assessed by phospholipid fatty acid was altered by restoration, but also varied by season and by site. Total soil carbon (C) and N and potential soil respiration did not differ between treatments, but N mineralization decreased while extractable nitrate and nitrification and N immobilization rate increased in restored compared with unrestored sites. The differences in soil chemistry and microbial community composition between unrestored and restored sites indicate that these soils are responsive, and therefore not resistant to feedbacks caused by changes in vegetation type. The resilience, or recovery, of these soils is difficult to assess in the absence of uninvaded control grasslands. However, the rapid changes in microbial and N cycling characteristics following removal of invasives in both grassland sites suggest that the soils are resilient to invasion. The lack of change in total C and N pools may provide a buffer that promotes resilience of labile pools and microbial community structure

High and low frequency dominated boundary layer transition through widely spaced discrete suction perforations

Boundary layer or wall-suction is a drag reduction technology with application to civil aircraft wings. Drag is reduced by increasing the extent of laminar flow across the boundary layer. Laminar flow has lower friction and form drag compared to turbulent flow. Wall-suction works by accelerating the air towards the surface of the wing, which has a stabilising effect on disturbances in the boundary layer; it also reduces the boundary layer thickness and thus the Reynolds number. In practice, this accelerated air must permeate through discrete pores in the surface. This creates local three-dimensional flow structures, which have been known to destabilise the flow and reduce the extent of laminar flow over wings, typically when the suction mass flow-rate is high. When this occurs the wall suction is said to be in a state of ‘over-suction’. In this work a set of experimental studies were performed on the problem of ‘over-suction’ for large arrays of suction perforations (in a widely spaced configuration), and for an isolated single suction perforation. It was found that the suction introduced a low frequency disturbance, this disturbance was found to grow (in amplitude) proportional to the suction rate. Furthermore, it was found that this low frequency was attenuated down-stream of the suction perforations, unless a pre-established N-type transition front was located close to the suction array. In this case the low-frequency was seen to interact with the N-type transition front, causing it to move upstream when at high suction rates.The amplitude of the low frequency also appeared to be Reynolds number independent, suggesting it may be an inflectional instability. The low frequency was correlated with inflection points in the stream-wise velocity‘u’profile across the span ‘z’. It has also been correlated with inflection points in the span-wise velocity ‘w’ profile across the wall-normal ‘y’. In the absence of any pre-established transition front, a high frequency disturbance was found to dominate the ‘over-suction’ process. This high frequency was found to only appear when the suction mass flow rate was sufficiently high, whereas the low frequency was found at all suction rates, and grew proportionally the non-dimensional suction mass flow-rate. This high frequency was also correlated with inflection points in the stream-wise velocity ‘u’ profile across the span‘z’. It has also been correlated with inflection points in the stream-wise velocity ‘u’ profile across the wall-normal ‘y’

The alpha 1/beta 1 and alpha 6/beta 1 integrin heterodimers mediate cell attachment to distinct sites on laminin.

This study was undertaken to determine the roles of individual alpha/beta 1 integrin heterodimers in promoting cellular interactions with the different attachment-promoting domains of laminin (LN). To do this, antibodies to the integrin beta 1 subunit or to specific integrin alpha subunits were tested for effects on cell attachment to LN, to elastase fragments E1-4 and E1, derived from the short arms and core of LN's cruciform structure, and to fragment E8 derived from the long arm of this structure. The human JAR choriocarcinoma cells used in this study attached to LN and to fragments E1 and E8. Attachment to E1-4 required a much higher substrate coating concentration, suggesting that it is a poor substrate for JAR cell attachment. The ability of cells to attach to different LN domains suggested the presence of more than one LN receptor. These multiple LN receptors were shown to be beta 1 integrin heterodimers because antibodies to the integrin beta 1 subunit inhibited attachment of JAR cells to LN and its three fragments. To identify the individual integrin alpha/beta 1 heterodimers that mediate interactions with these LN domains, mAbs specific for individual beta 1 heterodimers in human cells were used to study JAR cell interactions with LN and its fragments. An anti-alpha 6/beta 1-specific mAb, GoH3, virtually eliminated cell attachment to E8 and partially inhibited attachment to E1 and intact LN. Thus the major alpha 6/beta 1 attachment domain is present in fragment E8. An alpha 1/beta 1-specific mAb (S2G3) strongly inhibited cell attachment to collagen IV and partially inhibited JAR attachment to LN fragment E1. Thus, the alpha 1/beta 1 heterodimer is a dual receptor for collagen IV and LN, interacting with LN at a site in fragment E1. In combination, the anti-alpha 1- and anti-alpha 6-specific antibodies completely inhibited JAR cell attachment to LN and fragment E1. Thus, the alpha 1/beta 1 and alpha 6/beta 1 integrin heterodimers each function as LN receptors and act together to mediate the interactions of human JAR choriocarcinoma cells with LN

The post-test analysis of ablative materials Final report, 11 Jul. 1967 - 15 May 1968

Ablative materials examination before and after test firin

Molecular characterization of carbapenem-resistant Acinetobacter species in an Irish university hospital: predominance of Acinetobacter genomic species 3

A 30 month prospective study of Acinetobacter species encountered in the Central Pathology Laboratory of St James's Hospital, Dublin, Ireland, was conducted to investigate the prevalence and molecular epidemiology of carbapenem resistance in such isolates. Acinetobacter genomic species 3 (AG3) was found to be the predominant Acinetobacter species (45/114, 39 %) in our institution. A total of 11 % of all Acinetobacter species (12/114) and 22 % of AG3 isolates (10/45) were carbapenem resistant. Carbapenem resistance was mediated by Ambler class D beta-lactamase OXA-23 in all 12 isolates, with insertion sequence ISAba1 found upstream of bla(OXA-23). ISAba1 was also found upstream of bla(ADC-25), which encodes the enzyme AmpC, in an Acinetobacter baumannii isolate, and upstream of the aminoglycoside-acetyltransferase-encoding gene aacC2 in three AG3 isolates. Inter-species plasmidic transfer was most likely involved in the emergence and spread of bla(OXA-23) among the Acinetobacter isolates within our institution. The emergence of carbapenem resistance was associated not only with prior carbapenem use but also with the use of other antimicrobial agents, most notably beta-lactam/beta-lactamase-inhibitor combinations. The study demonstrated the emerging trend of carbapenem resistance in the wider context of the Acinetobacter genus, and reiterated the paramount importance of the prudent use of antimicrobial agents, stringent infection control measures and resistance surveillance of pathogens