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"Timofeev, Ivan"
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Special Issue: Soft Photonic Crystals and Metamaterials
2022
Soft matters include polymers, liquid crystals, colloids, biological tissues, and many smart materials [...].Soft matters include polymers, liquid crystals, colloids, biological tissues, and many smart materials [...].
Journal Article
Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton
by
Bikbaev, Rashid G.
,
Timofeev, Ivan V.
,
Maksimov, Dmitrii N.
in
Amplitudes
,
Angular resolution
,
Beam steering
2022
We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated.
Journal Article
Decompressive Craniectomy versus Craniotomy for Acute Subdural Hematoma
2023
In an international trial involving 450 patients with acute subdural hematoma, craniotomy (bone flap replaced) and decompressive craniectomy (bone flap left out) yielded similar disability-related outcomes at 12 months.
Journal Article
Fano feature induced by a bound state in the continuum via resonant state expansion
by
Timofeev, Ivan V.
,
Pankin, Pavel S.
,
Maksimov, Dmitrii N.
in
639/624/399/1022
,
639/624/400/1021
,
Anisotropy
2020
We consider light scattering by an anisotropic defect layer embedded into anisotropic photonic crystal in the spectral vicinity of an optical bound state in the continuum (BIC). Using a resonant state expansion method we derive an analytic solution for reflection and transmission amplitudes. The analytic solution is constructed via a perturbative approach with the BIC as the zeroth order approximation. The solution is found to describe the collapsing Fano feature in the spectral vicinity of the BIC. The findings are confirmed via comparison against direct numerical simulations with the Berreman transfer matrix method.
Journal Article
Epsilon-Near-Zero Absorber by Tamm Plasmon Polariton
2019
Two schemes of excitation of a Tamm plasmon polariton localized at the interface between a photonic crystal and a nanocomposite with near-zero effective permittivity have been investigated in the framework of the temporal coupled-mode theory. The parameters of the structure have been determined, which correspond to the critical coupling of the incident field with a Tamm plasmon polariton and, consequently, ensure the total absorption of the incident radiation by the structure. It has been established that the spectral width of the absorption line depends on the scheme of Tamm plasmon polariton excitation and the parameters of a nanocomposite film. The features of field localization at the Tamm plasmon polariton frequency for different excitation schemes have been examined. It has been demonstrated that such media can be used as narrowband absorbers based on Tamm plasmon polaritons localized at the interface between a photonic crystal and a nanocomposite with near-zero effective permittivity.
Journal Article
Defining metabolic abnormalities in acute human traumatic brain injury with cerebral microdialysis and multimodality monitoring
2025
We aimed to compare the prevalence and multimodal associations of mitochondrial dysfunction as defined by published cerebral-microdialysis-based criteria versus our novel multimodality-monitoring-based criteria in acute traumatic brain injury patients. We retrospectively analyzed neurocritical care monitoring data from 619 acute traumatic brain injury patients. Monitoring modalities included cerebral microdialysis, intracranial pressure, brain tissue oxygenation, cerebral perfusion pressure, and the pressure reactivity index. The cerebral-microdialysis-based criteria we compared combine an elevated lactate/pyruvate ratio (25 or 30) with raised concentrations of lactate (2.5 mM) or pyruvate (70 [mu]M or 120 [mu]M). Our multimodality-monitoring-based criteria comprise a consistent lactate/pyruvate ratio > 25 with intracranial pressure [less than or equal to] 20 mmHg, brain tissue oxygenation [greater than or equal to] 15 mmHg, a pressure reactivity index [less than or equal to] 0.3, and cerebral glucose [greater than or equal to] 1.0 mM. Across 592 analyzable patients, a lactate/pyruvate ratio > 25 was common, with a median prevalence of 48.9% (41.5% with consistency) and a U-shaped, bimodal distribution. A lactate/pyruvate ratio > 25 was associated with lower glucose and higher glycerol, and when accompanied by high pyruvate (> 120 [mu]M), this derangement was further distinguished by higher glutamate and cerebral perfusion pressure. Using multimodal criteria on a cohort of 268 patients, consistent mitochondrial dysfunction was identified in 25.7% to 41.0% of patients, often in the absence of other physiological derangements. Many acute traumatic brain injury patients constantly demonstrate neurometabolic derangements, among which clinical mitochondrial dysfunction is highly prevalent despite normal cerebral pressure, oxygenation, and perfusion. There is necessity for targeted, neurometabolic therapies in neurocritical care that address this abnormality.
Journal Article
Chiral-Selective Tamm Plasmon Polaritons
by
Bikbaev, Rashid G.
,
Chen, Kuo-Ping
,
Lin, Meng-Ying
in
Bragg reflectors
,
Cholesteric liquid crystals
,
Electric fields
2021
Chiral-selective Tamm plasmon polariton (TPP) has been investigated at the interface between a cholesteric liquid crystal and a metasurface. Different from conventional TPP that occurs with distributed Bragg reflectors and metals, the chiral–achiral TPP is successfully demonstrated. The design of the metasurface as a reflective half-wave plate provides phase and polarization matching. Accordingly, a strong localized electric field and sharp resonance are observed and proven to be widely tunable.
Journal Article
Trial of Decompressive Craniectomy for Traumatic Intracranial Hypertension
2016
In a trial comparing decompressive craniectomy with medical therapy in patients with traumatic brain injury and raised intracranial pressure refractory to medical therapy, decompressive craniectomy resulted in lower mortality and higher rates of vegetative state and severe disability.
After traumatic brain injury (TBI), intracranial pressure can be elevated owing to a mass effect from intracranial hematomas, contusions, diffuse brain swelling, or hydrocephalus.
1
Intracranial hypertension can lead to brain ischemia by reducing the cerebral perfusion pressure.
2
Intracranial hypertension after TBI is associated with an increased risk of death in most studies.
3
,
4
The monitoring of intracranial pressure and the administration of interventions to lower intracranial pressure are routinely used in patients with TBI, despite the lack of level 1 evidence.
5
Decompressive craniectomy is a surgical procedure in which a large section of the skull is removed and the underlying . . .
Journal Article
Characterising the dynamics of cerebral metabolic dysfunction following traumatic brain injury: A microdialysis study in 619 patients
by
Timofeev, Ivan
,
Stovell, Matthew G.
,
Hutchinson, Peter J.
in
Adult
,
Arterial Pressure
,
Biology and Life Sciences
2021
Traumatic brain injury (TBI) is a major cause of death and disability, particularly amongst young people. Current intensive care management of TBI patients is targeted at maintaining normal brain physiology and preventing secondary injury. Microdialysis is an invasive monitor that permits real-time assessment of derangements in cerebral metabolism and responses to treatment. We examined the prognostic value of microdialysis parameters, and the inter-relationships with other neuromonitoring modalities to identify interventions that improve metabolism. This was an analysis of prospective data in 619 adult TBI patients requiring intensive care treatment and invasive neuromonitoring at a tertiary UK neurosciences unit. Patients had continuous measurement of intracranial pressure (ICP), arterial blood pressure (ABP), brain tissue oxygenation (PbtO 2 ), and cerebral metabolism and were managed according to a standardized therapeutic protocol. Microdialysate was assayed hourly for metabolites including glucose, pyruvate, and lactate. Cerebral perfusion pressure (CPP) and cerebral autoregulation (PRx) were derived from the ICP and ABP. Outcome was assessed with the Glasgow Outcome Score (GOS) at 6 months. Relationships between monitoring variables was examined with generalized additive mixed models (GAMM). Lactate/Pyruvate Ratio (LPR) over the first 3 to 7 days following injury was elevated amongst patients with poor outcome and was an independent predictor of ordinal GOS (p<0.05). Significant non-linear associations were observed between LPR and cerebral glucose, CPP, and PRx (p<0.001 to p<0.05). GAMM models suggested improved cerebral metabolism (i.e. reduced LPR with CPP >70mmHg, PRx <0.1, PbtO 2 >18mmHg, and brain glucose >1mM. Deranged cerebral metabolism is an important determinant of patient outcome following TBI. Variations in cerebral perfusion, oxygenation and glucose supply are associated with changes in cerebral LPR and suggest therapeutic interventions to improve cerebral metabolism. Future prospective studies are required to determine the efficacy of these strategies.
Journal Article
Defining metabolic abnormalities in acute human traumatic brain injury with cerebral microdialysis and multimodality monitoring
2025
We aimed to compare the prevalence and multimodal associations of mitochondrial dysfunction as defined by published cerebral-microdialysis-based criteria versus our novel multimodality-monitoring-based criteria in acute traumatic brain injury patients.
We retrospectively analyzed neurocritical care monitoring data from 619 acute traumatic brain injury patients. Monitoring modalities included cerebral microdialysis, intracranial pressure, brain tissue oxygenation, cerebral perfusion pressure, and the pressure reactivity index. The cerebral-microdialysis-based criteria we compared combine an elevated lactate/pyruvate ratio (25 or 30) with raised concentrations of lactate (2.5 mM) or pyruvate (70 μM or 120 μM). Our multimodality-monitoring-based criteria comprise a consistent lactate/pyruvate ratio > 25 with intracranial pressure ≤ 20 mmHg, brain tissue oxygenation ≥ 15 mmHg, a pressure reactivity index ≤ 0.3, and cerebral glucose ≥ 1.0 mM.
Across 592 analyzable patients, a lactate/pyruvate ratio > 25 was common, with a median prevalence of 48.9% (41.5% with consistency) and a U-shaped, bimodal distribution. A lactate/pyruvate ratio > 25 was associated with lower glucose and higher glycerol, and when accompanied by high pyruvate (> 120 μM), this derangement was further distinguished by higher glutamate and cerebral perfusion pressure. Using multimodal criteria on a cohort of 268 patients, consistent mitochondrial dysfunction was identified in 25.7% to 41.0% of patients, often in the absence of other physiological derangements.
Many acute traumatic brain injury patients constantly demonstrate neurometabolic derangements, among which clinical mitochondrial dysfunction is highly prevalent despite normal cerebral pressure, oxygenation, and perfusion. There is necessity for targeted, neurometabolic therapies in neurocritical care that address this abnormality.
Journal Article