Thermoacoustic tomography with variable sound speed

We study the mathematical model of thermoacoustic tomography in media with a variable speed for a fixed time interval, greater than the diameter of the domain. In case of measurements on the whole boundary, we give an explicit solution in terms of a Neumann series expansion. We give necessary and sufficient conditions for uniqueness and stability when the measurements are taken on a part of the boundary

Time reversal in thermoacoustic tomography - an error estimate

The time reversal method in thermoacoustic tomography is used for approximating the initial pressure inside a biological object using measurements of the pressure wave made on a surface surrounding the object. This article presents error estimates for the time reversal method in the cases of variable, non-trapping sound speeds.Comment: 16 pages, 6 figures, expanded "Remarks and Conclusions" section, added one figure, added reference

Transplantation of ex vivo expanded limbal stem cells in neurotrophic keratopathy - a case report

Представяме клиничен случай на невротрофична кератопатия, асоциирана с унилатерална лимбална стволовоклетъчна инсуфициенция. Извършена бе трансплантация на автоложни ех vivo размножени лимбални стволови клетки. Използваните диагностични методи включват биомикроскопия, микробиологично изследване на секрет от конюнктива и роговична лезия, полимеразно верижна реакция на преднокамерна течност за херпес вирусна ДНК, оптична кохерентна томография на преден очен сегмент. Поради липсата на подобрение след консервативно лечение се проведе минимално инвазивиа лимбална биопсия и трансплантация на амниотична мембрана. Получените автоложни стволови клетки бяха размножени ех vivo по иновативен протокол без ксенобиотични продукти с преносител нативна амниотична мембрана. След получаване на достатъчно епителни слоеве ех vivo, се направи биологично покритие с готовия трансплантат. Постоперативно роговичната повърхност бе напълно епителизирана и зрителната острота се подобри значително. Наблюдава се регрес на неоваскуларните съдове и всички симптоми на хронично възпаление се облекчиха. Трансплантацията на автоложни ех vivo размножени лимбални стволови клетки с преностител амниотична мембрана може да бъде ефективен метод за лечение на невротрофична кератопатия, асоциирана с лимбална стволовоклетъчна инсуфициенция.We present a case of neurotrophic keratopathy associated with limbal stem cell deficiency, treated by transplantation of autologous ex vivo expanded limbal stem cells. The applied diagnostic methods include slit-lamp examination, microbiological samples from conjunctiva and corneal lesion, polymerase chain reaction of aqueous humor for herpes virus DNA, anterior segment optical coherence tomography. Since no improvement was observed with conservative treatment, a minimally invasive limbal biopsy and transplantation of amniotic membrane were performed. The collected autologous limbal stem cells were expanded ex vivo using an innovative protocol without xenobiotic products on intact amniotic membrane. After sufficient epithelial layers were obtained ex vivo the graft was transplanted on the ocular surface of the patient. Postoperatively the corneal surface was completely covered by epithelium, visual acuity improved significantly. Regression of neovascular vessels was observed and all symptoms of chronic inflammation were alleviated. Transplantation of ex vivo expanded limbal stem cells on amniotic membrane can be an effective treatment method for neurotrophic keratopathy, associated with limbal stem cell deficiency

Quantitative Photo-acoustic Tomography with Partial Data

Photo-acoustic tomography is a newly developed hybrid imaging modality that combines a high-resolution modality with a high-contrast modality. We analyze the reconstruction of diffusion and absorption parameters in an elliptic equation and improve an earlier result of Bal and Uhlmann to the partial date case. We show that the reconstruction can be uniquely determined by the knowledge of 4 internal data based on well-chosen partial boundary conditions. Stability of this reconstruction is ensured if a convexity condition is satisfied. Similar stability result is obtained without this geometric constraint if 4n well-chosen partial boundary conditions are available, where $n$ is the spatial dimension. The set of well-chosen boundary measurements is characterized by some complex geometric optics (CGO) solutions vanishing on a part of the boundary.Comment: arXiv admin note: text overlap with arXiv:0910.250

pH-triggered pore-forming peptides with strong composition-dependent membrane selectivity

Peptides that self-assemble into nanometer-sized pores in lipid bilayers could have utility in a variety of biotechnological and clinical applications if we can understand their physical chemical properties and learn to control their membrane selectivity. To empower such control, we have used synthetic molecular evolution to identify the pH-dependent delivery peptides, a family of peptides that assemble into macromolecule-sized pores in membranes at low peptide concentration but only at pH < ∼6. Further advancements will also require better selectivity for specific membranes. Here, we determine the effect of anionic headgroups and bilayer thickness on the mechanism of action of the pH-dependent delivery peptides by measuring binding, secondary structure, and macromolecular poration. The peptide pHD15 partitions and folds equally well into zwitterionic and anionic membranes but is less potent at pore formation in phosphatidylserine-containing membranes. The peptide also binds and folds similarly in membranes of various thicknesses, but its ability to release macromolecules changes dramatically. It causes potent macromolecular poration in vesicles made from phosphatidylcholine with 14 carbon acyl chains, but macromolecular poration decreases sharply with increasing bilayer thickness and does not occur at any peptide concentration in fluid bilayers made from phosphatidylcholine lipids with 20-carbon acyl chains. The effects of headgroup and bilayer thickness on macromolecular poration cannot be accounted for by the amount of peptide bound but instead reflect an inherent selectivity of the peptide for inserting into the membrane-spanning pore state. Molecular dynamics simulations suggest that the effect of thickness is due to hydrophobic match/mismatch between the membrane-spanning peptide and the bilayer hydrocarbon. This remarkable degree of selectivity based on headgroup and especially bilayer thickness is unusual and suggests ways that pore-forming peptides with exquisite selectivity for specific membranes can be designed or evolved

Thermoacoustic tomography arising in brain imaging

We study the mathematical model of thermoacoustic and photoacoustic tomography when the sound speed has a jump across a smooth surface. This models the change of the sound speed in the skull when trying to image the human brain. We derive an explicit inversion formula in the form of a convergent Neumann series under the assumptions that all singularities from the support of the source reach the boundary

Hidden Markov Models and their Application for Predicting Failure Events

We show how Markov mixed membership models (MMMM) can be used to predict the degradation of assets. We model the degradation path of individual assets, to predict overall failure rates. Instead of a separate distribution for each hidden state, we use hierarchical mixtures of distributions in the exponential family. In our approach the observation distribution of the states is a finite mixture distribution of a small set of (simpler) distributions shared across all states. Using tied-mixture observation distributions offers several advantages. The mixtures act as a regularization for typically very sparse problems, and they reduce the computational effort for the learning algorithm since there are fewer distributions to be found. Using shared mixtures enables sharing of statistical strength between the Markov states and thus transfer learning. We determine for individual assets the trade-off between the risk of failure and extended operating hours by combining a MMMM with a partially observable Markov decision process (POMDP) to dynamically optimize the policy for when and how to maintain the asset.Comment: Will be published in the proceedings of ICCS 2020; @Booklet{EasyChair:3183, author = {Paul Hofmann and Zaid Tashman}, title = {Hidden Markov Models and their Application for Predicting Failure Events}, howpublished = {EasyChair Preprint no. 3183}, year = {EasyChair, 2020}

How MOOC Reality Informs Distance Education, Online Learning, and Connectivism

In this paper, we draw from our experience as designers, instructors, and researchers in the second edition of a Massive Open Online Course (MOOCs) called Creativity, Innovation, and Change (CIC) 2.0 to discuss MOOC interactions. Since the CIC 2.0 MOOC was inspired by the tenets of connectivism, we employed connectivism and its four main conceptual components (autonomy, diversity, openness, and connectedness) to discuss these empirical findings from a theoretical perspective. We build our argument on the four levels of interactions (interactions with instructors, learners, course materials, and the interface) traditionally used in the field of distance education and online learning and look at the clashes between the original concepts of connectivism and cMOOCs on one hand and traditional educational concepts, particularly interactions and group work, on the other. This study discusses how MOOC interactions reveal that the four components of connectivism are more complex than originally conceptualized. This complexity can be summarized as follows: a) learner autonomy is more complex in MOOC reality; students are relatively more autonomous but not as originally conceptualized since the role of teachers remains unchanged when student interactions with course content and assessment are considered; b) diversity and openness are also more complex since peer interaction and open networks do not exhibit dynamics and importance as predicted, especially in certain participation behaviors and in MOOC pathways; and c) also, the four connectivism components are not mutually inclusive, and their interaction is not as predicted

Transplantation of ex vivo expanded limbal stem cells

Цел : Цел на настоящото проучване е да се изследват възможностите на трансплантацията на ех vivo размножени автоложни лимбални епителни стволови клетки като метод за лечение на повърхностни очни заболявания. Материали и методи: Трансплантации на автоложни ех vivo размножени стволови клетки бяха извършени на четирима пациенти на средна възраст 56.5 години преминали през Клиника по Очни болести към УМБАЛ "Александровска". Всички те демонстрираха клинични белези на унилатерална лимбална стволовоклетъчна инсуфициенция, асоциирана с трофични заболявания на очната повърхност, която бе демонстрирана чрез импресионна цитология. След получаване на информирано съгласие бе проведена минимално инвазивиа лимбална биопсия. Получените материали бяха обработени по иновапiВен протокол за клетъчни култури без употреба на ксенобиотични продукти. Четиринадесет дни по-късно бе направено биологично покритие с готовия трансплантат. Проследяване на състоянието се извърши чрез оптична кохерентна томография на преден очен сегмент преди и след трансплантацията. Критериите з a успех от трансплантацията на ех vivo размножени стволови клетки включват: 1. пълна епителизация на роговичната повърхност; 2. редукция на неоваскуларизацията или пълното ѝ изчезване; 3. възстановяване на нормални прозрачност, дебелина и рефлекс на роговицата; 4. подобрение на зрителната острота. Резултати : При всички пациенти се наблюдава подобрение на клиничната картина и субективните оплаквания. При трИ!Vш от изследваните бяха изпълнени четирите критерия за успешна трансплантация. При един от случаите не бе отчетено подобрение в зрителната острота, поради засягане на зрителния нерв от туморен процес. Не се наблюдаваха реакции на отхвърляне на трансплантата. Лимбалната биопсия не индуцира инсуфициенция на донорното око. Изводи : Трансплантацията на ех vivo размножени автоложни лимбални стволови клетки е ефективен и безопасен метод за възстановяване на очната повърхност, който може да бъде приложен при различни заболявания, асоциирани с лимбална стволовоклетъчна инсуфициенция.Purpose: To investigate the application of autologous ex vivo expanded limbal stem cell transplantation in the management of ocular surface disease. Materials and methods: Autologous ex vivo expanded stem cells were transplanted to four patients with mean age 56.5 years from the Depmtment of Ophthalmology, University Hospital Alexandrovska. All patients presented signs of unilateral limbal stem cell deficiency, associated with trophic disease of the ocular surface, which was demonstrated on impression cytology. After informed consent was obtained a minimally invasive limbal biopsy was performed. The limbal materials were cultured using a novel protocol without additional xenobiotic products. The grafts were transplanted after fourteen days. Anterior segment optical coherence tomography before and after the intervention was used for assessment of the condition. Success of the procedure was defined as 1. Complete epithelialization of the corneal surface, 2. partial or complete reduction of neovascularization, 3. achieving normal corneal transparency, thickness and reflex, 4. visual acuity improvement. Results: Clinical recovery was observed in all patients, as well as improvement of subjective ocular comfort. In three of the cases all four success criteria were met. Visual acuity of one patient did not change, due to neoplastic process, pervading the optic nerve. No graft rejection reactions were observed. Limbal biopsy did not induce limbal stem cell deficiency in the donor eye. Conclusion: Transplantation of autologous ex vivo expanded limbal stem cells is an effective and safe method for ocular surface reconstruction, which can be applied in different conditions, associated with limbal stem cell deficiency