An interband cascade laser (ICL) operating at 3.7 μm has been used to perform multimode absorption spectroscopy, MUMAS, at scan rates up to 10 kHz. Line widths of individual modes in the range 10-80 MHz were derived from isolated lines in the MUMAS signatures of HCl. MUMAS data for methane covering a spectral range of 30 nm yielded a detection level of 30 μbar·m for 1 s measurement time at 100 Hz. Simultaneous detection of methane, acetylene, and formaldehyde in a gas mixture containing all three species is reported.
or superluminescent diodes, can be used but have limited spectral resolution [2][3][4]. Methods based on correlation spectroscopy, COSPEC, provide a convenient method of detecting multiple gases but require a reference cell, at the same temperature and pressure as the target sample, for each species being detected [5,6]. The COSPEC technique, employing multi-mode lasers, has also been used for simultaneous detection of CO and CO 2 , thus demonstrating multi-species detection capability [7].The emerging spectroscopic techniques based on femtosecond frequency combs utilize the very broad spectrum of the light emitted by mode-locked lasers as the source for absorption spectroscopy. The modes are densely packed in frequency space and provide ultra-stable and precisely determined frequency markers [8]. The basic technique requires highly dispersive instruments to detect the absorption features of each species. Thus, spectral coverage or spectral resolution is compromised, and the systems are often complex, expensive, and unsuited to field applications. The fs-combs usually span the visible and near-infrared regions but, mid-infrared combs have been generated using difference frequency generating schemes or directly using quantum cascade lasers with parametric coupling by four-wave mixing processes in the gain media [9-12]. Alternatively, the multiple modes of Fabry-Perot-type QCL cavities can be used, and by use of heterodyne methods, the spectral information can be effectively studied in the radio frequency, RF, region [13]. Most manifestations so far reported used fixed frequency modes, and so resolution is constrained by the inter-mode frequency interval of the modes in the mid-infrared. The overall bandwidth will be limited by the bandwidth of the RF detectors. Scanning of the mid-infrared modes requires that the phase stability of the laser and the local oscillator laser be maintained during the scanning. Spectroscopic applications of scanned Abstract Multi-mode absorption spectroscopy of ammonia and methane at 3.3 μm has been demonstrated using a source of multi-mode mid-infrared radiation based on difference frequency generation. Multi-mode radiation at 1.56 μm from a diode-pumped Er:Yb:glass laser was mixed with a single-mode Nd:YAG laser at 1.06 μm in a periodically poled lithium niobate crystal to produce multimode radiation in the region of 3.3 μm. Detection, by direct multi-mode absorption, of NH 3 and CH 4 is reported for each species individually and also simultaneously in mixtures allowing measurements of partial pressures of each species.
BackgroundWhile it is has been proven that tranexamic acid (TXA) reduces blood loss in primary total hip and knee arthroplasty (THA and TKA), there is little published evidence on the use of TXA beyond 3 h post-operatively. Most blood loss occurs after wound closure and the primary aim of this study is to determine if the use of oral TXA post-operatively for up to 24 h will reduce calculated blood loss at 48 h beyond an intra-operative intravenous bolus alone following primary THA and TKA. To date, most TXA studies have excluded patients with a history of thromboembolic disease.Methods/designThis is a phase IV, single-centred, open-label, parallel-group, randomised controlled trial. Participants are randomised to one of three groups: group 1, an intravenous (IV) bolus of TXA peri-operatively plus oral TXA post-operatively for 24 h; group 2, an IV bolus of TXA peri-operatively or group 3, standard care (no TXA). Eligible participants, including those with a history of thromboembolic disease, are allocated to these groups with a 2:2:1 allocation ratio. The primary outcome is the indirectly calculated blood loss 48 h after surgery. Researchers and patients are not blinded to the treatment; however, staff processing blood samples are. Originally 1166 participants were required to complete this study, 583 THA and 583 TKA. However, following an interim analysis after 100 THA and 100 TKA participants had been recruited to the study, the data monitoring ethics committee recommended stopping group 3 (standard care).DiscussionTRAC-24 will help to determine whether an extended TXA dosing regimen can further reduce blood loss following primary THA and TKA. By including patients with a history of thromboembolic disease, this study will add to our understanding of the safety profile of TXA in this clinical situation.Trial registrationISRCTN registry, ISRCTN58790500. Registered on 3 June 2016, EudraCT: 2015–002661-36.Electronic supplementary materialThe online version of this article (10.1186/s13063-018-2784-3) contains supplementary material, which is available to authorized users.
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