Faster-than-light effects and negative group delays in optics and electronics, and their applications

Recent manifestations of apparently faster-than-light effects confirmed our predictions that the group velocity in transparent optical media can exceed c. Special relativity is not violated by these phenomena. Moreover, in the electronic domain, the causality principle does not forbid negative group delays of analytic signals in electronic circuits, in which the peak of an output pulse leaves the exit port of a circuit before the peak of the input pulse enters the input port. Furthermore, pulse distortion for these superluminal analytic signals can be negligible in both the optical and electronic domains. Here we suggest an extension of these ideas to the microelectronic domain. The underlying principle is that negative feedback can be used to produce negative group delays. Such negative group delays can be used to cancel out the positive group delays due to transistor latency (e.g., the finite RC rise time of MOSFETS caused by their intrinsic gate capacitance), as well as the propagation delays due to the interconnects between transistors. Using this principle, it is possible to speed up computer systems.Comment: 13 pages, 5 figures, 2001 Photonic West Plenary Tal

Real-time Spectroscopy with Sub-GHz Resolution using Amplified Dispersive Fourier Transformation

Dispersive Fourier transformation is a powerful technique in which spectral information is mapped into the time domain using chromatic dispersion. It replaces a spectrometer with an electronic digitizer, and enables real-time spectroscopy. The fundamental problem in this technique is the trade-off between the detection sensitivity and spectral resolution, a limitation set by the digitizer's bandwidth. This predicament is caused by the power loss associated with optical dispersion. We overcome this limitation using Raman amplified spectrum-to-time transformation. An extraordinary loss-less -11.76 ns/nm dispersive device is used to demonstrate single-shot gas absorption spectroscopy with 950 MHz resolution--a record in real-time spectroscopy.Comment: The following article has been accepted by Applied Physics Letter

Periodically-Poled Silicon [Updated]

We propose a new class of photonic devices based on periodic stress fields in silicon that enable second-order nonlinearity as well as quasi-phase matching. Periodically-poled silicon (PePSi) adds the periodic poling capability to silicon photonics, and allows the excellent crystal quality and advanced manufacturing capabilities of silicon to be harnessed for devices based on second-order nonlinear effects. As an example of the utility of the PePSi technology, we present simulations showing that mid-wave infrared radiation can be efficiently generated through difference frequency generation from near-infrared with a conversion efficiency of 50%. This technology can also be implemented with piezoelectric material, which offers the capability to dynamically control the X(2) nonlinearity.Comment: 11 pages, 4 figure

Anticipating pulmonary complications after thoracotomy: the FLAM Score

OBJECTIVE: Pulmonary complications after thoracotomy are the result of progressive changes in the respiratory status of the patient. A multifactorial score (FLAM score) was developed to identify postoperatively patients at higher risk for pulmonary complications at least 24 hours before the clinical diagnosis. METHODS: The FLAM score, created in 2002, is based on 7 parameters (dyspnea, chest X-ray, delivered oxygen, auscultation, cough, quality and quantity of bronchial secretions). To validate the FLAM score, we prospectively calculated scores during the first postoperative week in 300 consecutive patients submitted to posterolateral thoracotomy. RESULTS: During the study, 60 patients (20%) developed pulmonary complications during the postoperative period. The FLAM score progressively increased in complicated patients until the fourth postoperative day (mean 13.5 ± 11.9). FLAM scores in patients with complications were significantly higher (p < 0.05) at least 24 hours before the clinical diagnosis of complication, compared to FLAM scores in uncomplicated patients. ROC curves analysis showed that the cut-off value of FLAM with the best sensitivity and specificity for pulmonary complications was 9 (area under the curve 0.97). Based on the highest FLAM scores recorded, 4 risk classes were identified with increasing incidence of pulmonary complications and mortality. CONCLUSION: Changes in FLAM score were evident at least 24 hours before the clinical diagnosis of pulmonary complications. FLAM score can be used to categorize patients according to risk of respiratory morbidity and mortality and could be a useful tool in the postoperative management of patients undergoing thoracotomy

Enhancing methane production from lignocellulosic biomass by combined steam‑explosion pretreatment and bioaugmentation with cellulolytic bacterium Caldicellulosiruptor bescii

Background: Biogas production from lignocellulosic biomass is generally considered to be challenging due to the recalcitrant nature of this biomass. In this study, the recalcitrance of birch was reduced by applying steam-explosion (SE) pretreatment (210 °C and 10 min). Moreover, bioaugmentation with the cellulolytic bacterium Caldicellulosiruptor bescii was applied to possibly enhance the methane production from steam-exploded birch in an anaerobic digestion (AD) process under thermophilic conditions (62 °C). Results: Overall, the combined SE and bioaugmentation enhanced the methane yield up to 140% compared to untreated birch, while SE alone contributed to the major share of methane enhancement by 118%. The best methane improvement of 140% on day 50 was observed in bottles fed with pretreated birch and bioaugmentation with lower dosages of C. bescii (2 and 5% of inoculum volume). The maximum methane production rate also increased from 4-mL CH4/ g VS (volatile solids)/day for untreated birch to 9-14-mL CH4/ g VS/day for steam-exploded birch with applied bioaugmentation. Bioaugmentation was particularly effective for increasing the initial methane production rate of the pretreated birch yielding 21-44% more methane than the pretreated birch without applied bioaugmentation. The extent of solubilization of the organic matter was increased by more than twofold when combined SE pretreatment and bioaugmentation was used in comparison with the methane production from untreated birch. The beneficial effects of SE and bioaugmentation on methane yield indicated that biomass recalcitrance and hydrolysis step are the limiting factors for efficient AD of lignocellulosic biomass. Microbial community analysis by 16S rRNA amplicon sequencing showed that the microbial community composition was altered by the pretreatment and bioaugmentation processes. Notably, the enhanced methane production by pretreatment and bioaugmentation was well correlated with the increase in abundance of key bacterial and archaeal communities, particularly the hydrolytic bacterium Caldicoprobacter, several members of syntrophic acetate oxidizing bacteria and the hydrogenotrophic Methanothermobacter. Conclusion: Our findings demonstrate the potential of combined SE and bioaugmentation for enhancing methane production from lignocellulosic biomass

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries