34 research outputs found
Tomonaga-Luttinger parameters for quantum wires
The low-energy properties of a homogeneous one-dimensional electron system
are completely specified by two Tomonaga-Luttinger parameters and
. In this paper we discuss microscopic estimates of the values of
these parameters in semiconductor quantum wires that exploit their relationship
to thermodynamic properties. Motivated by the recognized similarity between
correlations in the ground state of a one-dimensional electron liquid and
correlations in a Wigner crystal, we evaluate these thermodynamic quantities in
a self-consistent Hartree-Fock approximation. According to our calculations,
the Hartree-Fock approximation ground state is a Wigner crystal at all electron
densities and has antiferromagnetic order that gradually evolves from
spin-density-wave to localized in character as the density is lowered. Our
results for are in good agreement with weak-coupling perturbative
estimates at high densities, but deviate strongly at low
densities, especially when the electron-electron interaction is screened at
long distances. vanishes at small carrier density
whereas we conjecture that when , implying that
should pass through a minimum at an intermediate density.
Observation of such a non-monotonic dependence on particle density would allow
to measure the range of the microscopic interaction. In the spin sector we find
that the spin velocity decreases with increasing interaction strength or
decreasing . Strong correlation effects make it difficult to obtain fully
consistent estimates of from Hartree-Fock calculations. We
conjecture that v_{\sigma}/\vf\propto n/V_0 in the limit where
is the interaction strength.Comment: RevTeX, 23 pages, 8 figures include
Constructional change in Old and Middle English Copular Constructions and its impact on the lexicon
Applying the framework of Radical Construction Grammar to diachronic phenomena, the present paper examines Copular Constructions in Old and Middle English, with special attention to the loss of the Copula weorðan ‘become’. First we reconstruct the extension of the OE Verbs is, beon, weorðan and becuman to various types of Copular Constructions. We further argue that schematic Copular Constructions emerge in overlapping usage areas resulting from these developments, in which abstraction is made of the Copulas' particular aspectual semantics. These schematic Copular Constructions in turn undergo some changes themselves. In Middle English a Passive Construction developed out of an original Copula Construction involving Adjectival Participles. However, the constructional profile of weorðan comprised an association between Participial and Adjectival Subject Complements much stronger than in other copulas, and this conflicted with this development, with the archaisization of weorðan as a result. This process of archaisization was further strengthened by the takeover of Weak Verbs in -ian (type ealdian ‘become old’) by new copulas like becuman. In general, we show how diachronic construction grammar might account for the loss of a function word otherwise difficult to account for.3H05117
Predictive Value of Initial Triage Vital Signs for Critically Ill Older Adults
INTRODUCTION: Triage of patients is critical to patient safety, yet no clear information exists as to the utility of initial vital signs in identifying critically ill older emergency department (ED) patients. The objective of this study is to evaluate a set of initial vital sign thresholds as predictors of severe illness and injury among older adults presenting to the ED. METHODS: We reviewed all visits by patients aged 75 and older seen during 2007 at an academic ED serving a large community of older adults. Patients’ charts were abstracted for demographic and clinical information including vital signs, via automated electronic methods. We used bivariate analysis to investigate the relationship between vital sign abnormalities and severe illness or injury, defined as intensive care unit (ICU) admission or ED death. In addition, we calculated likelihood ratios for normal and abnormal vital signs in predicting severe illness or injury. RESULTS: 4,873 visits by patients aged 75 and above were made to the ED during 2007, and of these 3,848 had a complete set of triage vital signs. For these elderly patients, the sensitivity and specificity of an abnormal vital sign taken at triage for predicting death or admission to an ICU were 73% (66,81) and 50% (48,52) respectively (positive likelihood ratio 1.47 (1.30,1.60); negative likelihood ratio 0.54 (0.30,0.60). CONCLUSION: Emergency provider assessment and triage scores that rely primarily on initial vital signs are likely to miss a substantial portion of critically ill older adults
Predictive Value of Initial Triage Vital Signs for Critically Ill Older Adults
Introduction: Triage of patients is critical to patient safety, yet no clear information exists as to the utility of initial vital signs in identifying critically ill older emergency department (ED) patients. The objective of this study is to evaluate a set of initial vital sign thresholds as predictors of severe illness and injury among older adults presenting to the ED.Methods: We reviewed all visits by patients aged 75 and older seen during 2007 at an academic ED serving a large community of older adults. Patients’ charts were abstracted for demographic and clinical information including vital signs, via automated electronic methods. We used bivariate analysis to investigate the relationship between vital sign abnormalities and severe illness or injury, defined as intensive care unit (ICU) admission or ED death. In addition, we calculated likelihood ratios for normal and abnormal vital signs in predicting severe illness or injury.Results: 4,873 visits by patients aged 75 and above were made to the ED during 2007, and of these 3,848 had a complete set of triage vital signs. For these elderly patients, the sensitivity and specificity of an abnormal vital sign taken at triage for predicting death or admission to an ICU were 73% (66,81) and 50% (48,52) respectively (positive likelihood ratio 1.47 (1.30,1.60); negative likelihood ratio 0.54 (0.30,0.60).Conclusion: Emergency provider assessment and triage scores that rely primarily on initial vital signs are likely to miss a substantial portion of critically ill older adults. [West J Emerg Med. 2013;14(5):453–460.