552 research outputs found
Standard and Null Weak Values
Weak value (WV) is a quantum mechanical measurement protocol, proposed by
Aharonov, Albert, and Vaidman. It consists of a weak measurement, which is
weighed in, conditional on the outcome of a later, strong measurement. Here we
define another two-step measurement protocol, null weak value (NVW), and point
out its advantages as compared to WV. We present two alternative derivations of
NWVs and compare them to the corresponding derivations of WVs.Comment: 11 pages, 2 figures. To appear in Quantum Theory: A Two-Time Success
Story: Yakir Aharonov Festschrif
A parametric symmetry breaking transducer
Force detectors rely on resonators to transduce forces into a readable
signal. Usually these resonators operate in the linear regime and their signal
appears amidst a competing background comprising thermal or quantum
fluctuations as well as readout noise. Here, we demonstrate that a parametric
symmetry breaking transduction leads to a novel and robust nonlinear force
detection in the presence of noise. The force signal is encoded in the
frequency at which the system jumps between two phase states which are
inherently protected against phase noise. Consequently, the transduction
effectively decouples from readout noise channels. For a controlled
demonstration of the method, we experiment with a macroscopic doubly-clamped
string. Our method provides a promising new paradigm for high-precision force
detection.Comment: 7 pages, 5 figure
Predictors of hospital mortality among septic ICU patients with Acinetobacter spp. bacteremia: A cohort study
BACKGROUND: We hypothesized that among septic ICU patients with Acinetobacter spp. bacteremia (Ac-BSI), carbapenem-resistant Acinetobacter spp. (CRAc) increase risk for inappropriate initial antibiotic therapy (non-IAAT), and non-IAAT is a predictor of hospital death. METHODS: We conducted a retrospective cohort study of adult septic ICU patients with Ac-BSI. Non-IAAT was defined as exposure to initially prescribed antibiotics not active against the pathogen based on in vitro susceptibility testing, and having no exposure to appropriate antimicrobial treatment within 24 hours of drawing positive culture. We compared patients who died to those who survived, and derived regression models to identify predictors of hospital mortality and of non-IAAT. RESULTS: Out of 131 patients with Ac-BSI, 65 (49.6%) died (non-survivors, NS). NS were older (63 [51, 76] vs. 56 [45, 66] years, p = 0.014), and sicker than survivors (S): APACHE II (24 [19, 31] vs. 18 [13, 22], p < 0.001) and Charlson (5 [2, 8] vs. 3 [1, 6], p = 0.009) scores. NS were also more likely than S to require pressors (75.4% vs. 42.4%, p < 0.001) and mechanical ventilation (75.4% vs. 53.0%, p = 0.008). Both CRAc (69.2% vs. 47.0%, p = 0.010) and non-IAAT (83.1% vs. 59.1%, p = 0.002) were more frequent among NS than S. In multivariate analyses, non-IAAT emerged as an independent predictor of hospital death (risk ratio [RR] 1.42, 95% confidence interval [CI] 1.10-1.58), while CRAc was the single strongest predictor of non-IAAT (RR 2.66, 95% CI 2.43-2.72). CONCLUSIONS: Among septic ICU patients with Ac-BSI, non-IAAT predicts mortality. Carbapenem resistance appears to mediate the relationship between non-IAAT and mortality
Multidrug resistance, inappropriate empiric treatment and hospital mortality in Acinetobacter baumannii pneumonia and sepsis
Background: The relationship between multidrug resistance (MDR), inappropriate empiric therapy (IET), and
mortality among patients with Acinetobacter baumannii (AB) remains unclear. We examined it using a large
U.S. database.
Methods: We conducted a retrospective cohort study using the Premier Research database (2009ā2013) of 175 U.S.
hospitals. We included all adult patients admitted with pneumonia or sepsis as their principal diagnosis, or as a
secondary diagnosis in the setting of respiratory failure, along with antibiotic administration within 2 days of
admission. Only culture-confirmed infections were included. Resistance to at least three classes of antibiotics
defined multidrug-resistant AB (MDR-AB). We used logistic regression to compute the adjusted relative risk ratio
(RRR) of patients with MDR-AB receiving IET and IETās impact on mortality.
Results: Among 1423 patients with AB infection, 1171 (82.3 %) had MDR-AB. Those with MDR-AB were older
(63.7 Ā± 15.4 vs. 61.0 Ā± 16.9 years, p = 0.014). Although chronic disease burden did not differ between groups, the
MDR-AB group had higher illness severity than those in the non-MDR-AB group (intensive care unit 68.0 % vs. 59.
5 %, p < 0.001; mechanical ventilation 56.2 % vs. 42.1 %, p < 0.001). Patients with MDR-AB were more likely to
receive IET than those in the non-MDR-AB group (76.2 % MDR-AB vs. 13.8 % non-MDR-AB, p < 0.001). In a regression
model, MDR-AB strongly predicted receipt of IET (adjusted RRR 5.5, 95 % CI 4.0ā7.7, p < 0.001). IET exposure was
associated with higher hospital mortality (adjusted RRR 1.8, 95 % CI 1.4ā2.3, p < 0.001).
Conclusions: In this large U.S. database, the prevalence of MDR-AB among patients with AB infection was > 80 %.
Harboring MDR-AB increased the risk of receiving IET more than fivefold, and IET nearly doubled hospital mortality
Exploring 4D Quantum Hall Physics with a 2D Topological Charge Pump
The discovery of topological states of matter has profoundly augmented our
understanding of phase transitions in physical systems. Instead of local order
parameters, topological phases are described by global topological invariants
and are therefore robust against perturbations. A prominent example thereof is
the two-dimensional integer quantum Hall effect. It is characterized by the
first Chern number which manifests in the quantized Hall response induced by an
external electric field. Generalizing the quantum Hall effect to
four-dimensional systems leads to the appearance of a novel non-linear Hall
response that is quantized as well, but described by a 4D topological invariant
- the second Chern number. Here, we report on the first observation of a bulk
response with intrinsic 4D topology and the measurement of the associated
second Chern number. By implementing a 2D topological charge pump with
ultracold bosonic atoms in an angled optical superlattice, we realize a
dynamical version of the 4D integer quantum Hall effect. Using a small atom
cloud as a local probe, we fully characterize the non-linear response of the
system by in-situ imaging and site-resolved band mapping. Our findings pave the
way to experimentally probe higher-dimensional quantum Hall systems, where new
topological phases with exotic excitations are predicted
Determining Mortality Rates Attributable to Clostridium difficile Infection
To determine accuracy of measures of deaths attributable to Clostridium difficile infection, we compared 3 measures for 2007ā2008 in Ontario, Canada: death certificate; death within 30 days of infection; and panel review. Data on death within 30 days were more feasible than panel review and more accurate than death certificate data
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