Experimental and numerical study of multi-pulse picosecond laser ablation on 316†L stainless steel.

An experimental and numerical study on 10 ps laser ablation of 316 L stainless steel up to 400 hundred pulse exposure has been carried out. In this simulation, the material removal threshold temperature has been carefully discussed depending on the different ablation driving mechanisms. The influence of the instantaneous material removal has also been considered which will affect the calculation of the next pulse's absorption. For single-pulse ablation, the simulated ablation threshold Fsim = 0.26 J/cm2 is close to the fitted experimental result F0th = (0.29 ± 0.01) J/cm2. For multi-pulse ablation, the simulated ablation rate Rsim = 11.4 nm/pulse is close to the fitted experimental result Rexp = (12.4 ± 0.1) nm/pulse under 0.9 J/cm2 fluence, while the simulated ablation rate Rsim = 19.8 nm/pulse is slightly larger than the fitted experimental result Rexp = (16.1 ± 0.7) nm/pulse at 2.7 J/cm2, providing good agreement between theory and experiment for both single and multi-pulse ablation. This study could be used to predict the multi-pulse laser processing performance, especially with the help of a machine learning method to find the best parameters automatically.

The effect of dexmedetomidine and clonidine on the inflammatory response in critical illness: a systematic review of animal and human studies.

BACKGROUND: The α2 agonists, dexmedetomidine and clonidine, are used as sedative drugs during critical illness. These drugs may have anti-inflammatory effects, which might be relevant to critical illness, but a systematic review of published literature has not been published. We reviewed animal and human studies relevant to critical illness to summarise the evidence for an anti-inflammatory effect from α2 agonists. METHODS: We searched PubMed, the Cochrane library, and Medline. Animal and human studies published in English were included. Broad search terms were used: dexmedetomidine or clonidine, sepsis, and inflammation. Reference lists were screened for additional publications. Titles and abstracts were screened independently by two reviewers and full-text articles obtained for potentially eligible studies. Data extraction used a bespoke template given study diversity, and quality assessment was qualitative. RESULTS: Study diversity meant meta-analysis was not feasible so descriptive synthesis was undertaken. We identified 30 animal studies (caecal ligation/puncture (9), lipopolysaccharide (14), acute lung injury (5), and ischaemia-reperfusion syndrome (5)), and 9 human studies. Most animal (26 dexmedetomidine, 4 clonidine) and all human studies used dexmedetomidine. In animal studies, α2 agonists reduced serum and/or tissue TNFα (20 studies), IL-6 (17 studies), IL-1ß (7 studies), NFκB (6 studies), TLR4 (6 studies), and a range of other mediators. Timing and doses varied widely, but in many cases were not directly relevant to human sedation use. In human studies, dexmedetomidine reduced CRP (4 studies), TNFα (5 studies), IL-6 (6 studies), IL-1ß (3 studies), and altered several other mediators. Most studies were small and low quality. No studies related effects to clinical outcomes. CONCLUSION: Evidence supports potential anti-inflammatory effects from α2 agonists, but the relevance to clinically important outcomes is uncertain. Further work should explore whether dose relationships with inflammation and clinical outcomes are present which might be separate from sedation-mediated effects.

Imaging-based amplitude laser beam shaping for material processing by 2D reflectivity tuning of a spatial light modulator.

We have demonstrated an imaging-based amplitude laser-beam-shaping technique for material processing by 2D reflectivity tuning of a spatial light modulator. Intensity masks with 256 gray levels were designed to shape the input laser beam in the outline profile and inside intensity distribution. Squared and circular flattop beam shapes were obtained at the diffractive near-field and then reconstructed at an image plane of an f-theta lens (f∼100 mm). The observed intensity distribution inside the beam-shaping geometry was much more even than using binary masks. The ablation footprint well matches the desired beam shape.

Major incident preparedness in a post pandemic world: A survey of anaesthetists.

The COVID-19 pandemic profoundly changed anaesthetic and critical care departments across the UK and fulfilled the definition of a major incident for an extended period of time. It is regularly highlighted that individual and organisational readiness for major incident is inconsistent, as is support in the aftermath. Post-pandemic rates of anxiety and PTSD in healthcare staff have significantly increased, but we still have no embedded method of helping to prevent it. Clinical debriefing is an emerging tool with proven improved psychological outcomes for staff following an adverse event. We surveyed 354 anaesthetists of a range of grades and experiences prior to attending a webinar centred on major incident organisation, human factors and clinical debrief. While 73.8% knew where to access their hospital's major incident plan, only 16.8% had been trained in any form of clinical debrief. Only 29% had ever received any formal training in major incident management. It seems that the occurrence of major incidents is no longer a 'once in a career' event. The inconsistencies in training and preparedness shown in our survey highlight opportunities for our workforce to be more agile and subsequently better supported for the future.

Dying to be better: Outlining the growing benefits of palliative care training in intensive care medicine.

A core part of an intensivist's work involves navigating the challenges of End of Life Care. While rates of survival from critical illness have gradually improved, 15%-20% of our patients die during their hospital admission, and a further 20% die within a year. 80% of our patients lack capacity to express their wishes with regard to treatment escalation planning. The critical care unit can be an excellent place to provide a good death, however the very nature of critical illness provides some obstacles to this. Prognostic uncertainty, time-pressured critical decision making, and lack of meaningful contact with a patient and their loved ones are but a few. In this article, we compare the ethos of critical care and palliative care medicine and explore how training in both of these specialities could be brought closer together and more formalised such that the intensivists of the future are more strongly equipped with the skills to shape a critical care unit to overcome these challenges and provide the best care to these patients, many of whom may be in the final phase of their life.

Management of transgender patients in critical care.

As clinicians working in critical care, it is our duty to provide all of our patients with the high-quality care they deserve, regardless of their gender identity. The transgender community continues to suffer discrimination from the media, politicians and general public. As healthcare workers we often pride ourselves on our ability to safely care for all patients. However, there remains a distinct lack of understanding surrounding the care of critically ill transgender patients. This is likely in part because the specific care of transgender patients is not included in the Faculty of Intensive Care Medicine's, Royal College of Anaesthetists', Royal College of Physician's, or Royal College of Emergency Medicine's curriculum. There are several important considerations relevant for transgender patients in critical care including anatomical changes to the airway, alterations to respiratory and cardiovascular physiology and management of hormone therapy. Alongside this, there are simple but important social factors that exist, such as the use of patient pronouns and ensuring admittance to correctly gendered wards. In this review we will address the key points relevant to the care of transgender patients in critical care and provide suggestions on how education on the subject may be improved.

The perioperative management of transgender patients: a knowledge gap we can no longer ignore.

Recent years have seen an increase in the number of people openly identifying as transgender in the UK, with current estimates ranging between 200 000 and 600 000 individuals. There has also been an increase in the number of patients undergoing both medical and surgical gender-affirming treatment. There are several important, specific considerations that perioperative clinicians must be aware of when caring for transgender patients, including changes to the airway, potential respiratory and cardiovascular complications, and the management of hormone therapy. Alongside this, important general considerations include the correct use of patient pronouns and ensuring patients are admitted to correctly gendered wards. Despite the need for these considerations, the perioperative management of transgender patients is not covered in the Royal College of Anaesthetists' curriculum; to date, no national guidelines exist on the subject. This article discusses some of the key, specific perioperative considerations relevant to transgender patients, and highlights the need for national guidelines and improved education on the subject.

Pulse Burst Generation and Diffraction with Spatial Light Modulators for Dynamic Ultrafast Laser Materials Processing.

A pulse burst optical system has been developed, able to alter an energetic, ultrafast 10 ps, 5 kHz output pulse train to 323 MHz intra-burst frequency at the fundamental 5 kHz repetition rate. An optical delay line consisting of a beam-splitting polariser cube, mirrors, and waveplates transforms a high-energy pulse into a pulse burst, circulating around the delay line. Interestingly, the reflected first pulse and subsequent pulses from the delay line have orthogonal linear polarisations. This fact allows independent modulation of these pulses using two-phase-only Spatial Light Modulators (SLM) when their directors are also aligned orthogonally. With hybrid Computer Generated Holograms (CGH) addressed to the SLMs, we demonstrate simultaneous multi-spot periodic surface micro-structuring on stainless steel with orthogonal linear polarisations and cylindrical vector (CV) beams with Radial and Azimuthal polarisations. Burst processing produces a major change in resulting surface texture due to plasma absorption on the nanosecond time scale; hence the ablation rates on stainless steel with pulse bursts are always lower than 5 kHz processing. By synchronising the scan motion and CGH application, we show simultaneous independent multi-beam real-time processing with pulse bursts having orthogonal linear polarisations. This novel technique extends the flexibility of parallel beam surface micro-structuring with adaptive optics.

Backward Flux Re-Deposition Patterns during Multi-Spot Laser Ablation of Stainless Steel with Picosecond and Femtosecond Pulses in Air.

We report on novel observations of directed re-deposition of ablation debris during the ultrafast laser micro-structuring of stainless steel in the air with multi-beams in close proximity on the surface. This interesting phenomenon is observed with both 10 ps and 600 fs NIR laser pulses at 5 kHz repetition rate. Ablation spot geometries could be altered with the use of beam splitting optics or a phase-only Spatial Light modulator. At low fluence (F ~ 1.0 J cm-2) and pulse exposure of a few hundred pulses, the debris appears as concentrated narrow "filaments" connecting the ablation spots, while at higher fluence, (F ~ 5.0 J cm-2) energetic jets of material emanated symmetrically along the axes of symmetry, depositing debris well beyond the typical re-deposition radius with a single spot. Patterns of backward re-deposition of debris to the surface are likely connected with the colliding shock waves and plasma plumes with the ambient air causing stagnation when the spots are in close proximity. The 2D surface debris patterns are indicative of the complex 3D interactions involved over wide timescales during ablation from picoseconds to microseconds.

Laser-Material Interactions of High-Quality Ultrashort Pulsed Vector Vortex Beams.

Diffractive multi-beams based on 1 × 5 and 2 × 2 binary Dammann gratings applied to a spatial light modulator (SLM) combined with a nanostructured S-wave plate have been used to generate uniform multiple cylindrical vector beams with radial and azimuthal polarizations. The vector quality factor (concurrence) of the single vector vortex beam was found to be C = 0.95 ± 0.02, hence showing a high degree of vector purity. The multi-beams have been used to ablate polished metal samples (Ti-6Al-4V) with laser-induced periodic surface structures (LIPSS), which confirm the polarization states unambiguously. The measured ablation thresholds of the ring mode radial and azimuthal polarizations are close to those of a Gaussian mode when allowance is made for the expected absolute intensity distribution of a ring beam generated from a Gaussian. In addition, ring mode vortex beams with varying orbital angular momentum (OAM) exhibit the same ablation threshold on titanium alloy. Beam scanning with ring modes for surface LIPSS formation can increase micro-structuring throughput by optimizing fluence over a larger effective beam diameter. The comparison of each machined spot was analysed with a machine learning method-cosine similarity-which confirmed the degree of spatial uniformity achieved, reaching cosθ > 0.96 and 0.92 for the 1 × 5 and 2 × 2 arrays, respectively. Scanning electron microscopy (SEM), optical microscopy and white light surface profiling were used to characterize and quantify the effects of surface modification.

Transition from fractional to classical Stokes-Einstein behaviour in simple fluids.

An optical technique for tracking single particles has been used to evaluate the particle diameter at which diffusion transitions from molecular behaviour described by the fractional Stokes-Einstein relationship to particle behaviour described by the classical Stokes-Einstein relationship. The results confirm a prior prediction from molecular dynamic simulations that there is a particle size at which transition occurs and show it is inversely dependent on concentration and viscosity but independent of particle density. For concentrations in the range 5 × 10-3 to 5 × 10-6 mg ml-1 and viscosities from 0.8 to 150 mPa s, the transition was found to occur in the diameter range 150-300 nm.