Quantum limited amplification with a nonlinear cavity detector

We consider the quantum measurement properties of a driven cavity with a Kerr-type nonlinearity which is used to amplify a dispersively coupled input signal. Focusing on an operating regime which is near a bifurcation point, we derive simple asymptotic expressions describing the cavity's noise and response. We show that the cavity's backaction and imprecision noise allow for quantum limited linear amplification and position detection only if one is able to utilize the sizeable correlations between these quantities. This is possible when one amplifies a non-resonant signal, but is not possible in QND qubit detection. We also consider the possibility of using the nonlinear cavity's backaction for cooling a mechanical mode.Comment: 15 pages, 6 figure

Weak Qubit Measurement with a Nonlinear Cavity: Beyond Perturbation Theory

We analyze the use of a driven nonlinear cavity to make a weak continuous measurement of a dispersively-coupled qubit. We calculate the backaction dephasing rate and measurement rate beyond leading-order perturbation theory using a phase-space approach which accounts for cavity noise squeezing. Surprisingly, we find that increasing the coupling strength beyond the regime describable by leading-order perturbation theory (i.e. linear response) allows one to come significantly closer to the quantum limit on the measurement efficiency. We interpret this behaviour in terms of the non-Gaussian photon number fluctuations of the nonlinear cavity. Our results are relevant to recent experiments using superconducting microwave circuits to study quantum measurement.Comment: 4+ pages, 2 figure

Can we quickly and thoroughly assess pain with the PACSLAC-II? : a convergent validity study in long-term care residents suffering from dementia.

Abstract : A previous study found that the modified version of the Pain Assessment Checklist for Seniors with Limited Ability to Communicate (PACSLAC-II) is a valid tool to assess pain in elderly individuals suffering from dementia and who are unable to communicate verbally. The primary objective of this study was to confirm the convergent validity of the PACSLAC-II using direct evaluation of long-term care residents in real-life situations, using two other well-validated pain assessment scales (i.e., PACSLAC and Pain Assessment in Advanced Dementia [PAINAD]). A secondary objective was to document and compare the time required to complete and score each assessment scale. During two potentially painful procedures (i.e., transfer/mobilization), 46 long-term care residents (mean age = 83 ± 10 years) suffering from dementia were observed by three independent evaluators, each using one of the assessment scales (randomly assigned). Correlational analyses and analysis of variance were used to evaluate the association between each scale and to compare scoring time. The PACSLAC (r = 0.61) and the PAINAD (r = 0.65) were both moderately associated with the PACSLAC-II (all p values < .001). The PAINAD's average scoring time (63 ± 19 seconds) was lower than the PACSLAC-II's (96 ± 2 seconds), which was lower than the PACSLAC's (135 ± 53 seconds) (all p values < .001). These results suggest that the PACSLAC-II is a valid tool for assessing pain in individuals with dementia. The time required to complete and score the PACSLAC-II was reasonable, supporting its usefulness in clinical settings

Investigation of the Fouling Effect on a Commercial Semi-Permeable Membrane in the Pressure Retarded Osmosis (PRO) Process

One of the main challenges for generating osmotic power by using PRO technology is the membrane fouling which reduces the permeate flux and consequently increases the cost and decreases the osmotic power generation. In this research, different feed waters with various qualities were used to investigate the effect of fouling on a commercial membrane in PRO mode in continuous conditions. Also, the fouling mechanisms were investigated in order to study the cleaning of the membrane in PRO mode in the future research. In addition, four classic fouling models such as complete blocking model (CBM), intermediate blocking model (IBM), standard blocking model (SBM) and cake filtration model (CFM) were used. Cake enhanced osmotic pressure as a new mechanism for osmotically driven membranes was studied as well. According to the results, the fouling rate when the draw solution was synthetic salt water followed the order of: untreated river water > multimedia sand filter > microfiltration > ultrafiltration effluents. The fouling rate in ultrafiltration and microfiltration effluents using sea water occurred faster compared to the results for untreated synthetic salt water. Complete fouling (permeate flux was negligible) occurred after 580 hours using feed water from ultrafiltration unit. It was observed that cake filtration and cake enhanced osmotic pressure were the main fouling mechanisms that governed the membrane fouling. These models could describe the membrane fouling in PRO processes

Compact secondary treatment train combining a lab-scale moving bed biofilm reactor and enhanced flotation processes

High-rate wastewater processes are receiving a renewed interest to obtain energy positive/efficient water resource recovery facilities. An innovative treatment train combining a high-rate moving bed biofilm reactor (HR-MBBR) with an enhanced flotation process was studied. The two objectives of this work were 1) to maximize the conversion of soluble organics to particulate matter in an HR-MBBR and 2) to maximize the particulate matter recovery from the HR-MBBR effluent by green chemicals to enhance biogas production by anaerobic digestion. To achieve these objectives, lab-scale MBBRs fed with synthetic soluble wastewater were operated at organic loading rates (OLRs) between 4 and 34 kg COD m−3 reactor d−1 corresponding to hydraulic retention times (HRTs) between 6 and 54 min. Colloidal and soluble chemical oxygen demand (COD) removal efficiency in the HR-MBBR increased with HRT to reach a plateau of 85% at an HRT longer than 27 min. Carrier clogging observed at an OLR higher than 16 kg COD m−3 d−1 (HRT < 13 min) resulted in about 23% loss in colloidal and soluble COD removal efficiency. Thus, the recommended parameters were between 22 and 37 min and between 6 and 10 kg COD m−3 d−1 for the HRT and the OLR, respectively, to maximize the conversion of soluble organics to particulate matter. Total suspended solids (TSS) recovery of 58–85% and 90–97% were achieved by enhanced flotation using green and unbiodegradable chemicals, respectively, corresponding to a TSS effluent concentration below 14 and 7 mg TSS/L. Among the synthetic polymers tested, a high molecular weight and low charge density cationic polyacrylamide was found to give the best results with less than 2 mg TSS/L in the clarified effluent (97% TSS recovery). Green chemicals, although performing slightly less for solids separation than unbiodegradable chemicals, achieved a mean TSS concentration of 10 ± 3 mg/L in the clarified effluent