Ionization Front Instabilities in Primordial H II Regions

Radiative cooling by metals in shocked gas mediates the formation of ionization front instabilities in the galaxy today that are responsible for a variety of phenomena in the interstellar medium, from the morphologies of nebulae to triggered star formation in molecular clouds. An important question in early reionization and chemical enrichment of the intergalactic medium is whether such instabilities arose in the H II regions of the first stars and primeval galaxies, which were devoid of metals. We present three-dimensional numerical simulations that reveal both shadow and thin-shell instabilities readily formed in primordial gas. We find that the hard UV spectra of Population III stars broadened primordial ionization fronts, causing H2 formation capable of inciting violent thin- shell instabilities in D-type fronts, even in the presence of intense Lyman-Werner flux. The high post- front gas temperatures associated with He ionization sustained and exacerbated shadow instabilities, unaided by molecular hydrogen cooling. Our models indicate that metals eclipsed H2 cooling in I-front instabilities at modest concentrations, from 0.001- 0.01 solar. We conclude that ionization front instabilities were prominent in the H II regions of the first stars and galaxies, influencing the escape of ionizing radiation and metals into the early universe.Comment: 13 pages, 11 figures, accepted by ApJ with minor revision

Synthesizing Certified Code

Code certification is a lightweight approach for formally demonstrating software quality. Its basic idea is to require code producers to provide formal proofs that their code satisfies certain quality properties. These proofs serve as certificates that can be checked independently. Since code certification uses the same underlying technology as program verification, it requires detailed annotations (e.g., loop invariants) to make the proofs possible. However, manually adding annotations to the code is time-consuming and error-prone. We address this problem by combining code certification with automatic program synthesis. Given a high-level specification, our approach simultaneously generates code and all annotations required to certify the generated code. We describe a certification extension of AutoBayes, a synthesis tool for automatically generating data analysis programs. Based on built-in domain knowledge, proof annotations are added and used to generate proof obligations that are discharged by the automated theorem prover E-SETHEO. We demonstrate our approach by certifying operator- and memory-safety on a data-classification program. For this program, our approach was faster and more precise than PolySpace, a commercial static analysis tool

Treating GM1 Gangliosidosis With Ex Vivo Hematopoietic Stem Cell Gene Therapy Without Using Total Body Irradiation: A Masters Thesis

GM1 gangliosidosis is an autosomal recessive lysosomal storage disease, caused by a deficiency in the enzyme β-galactosidase. The disease affects the CNS, liver, kidney, heart and skeletal system, leading to severe neurodegeneration and death. We propose to treat this disorder using ex vivo hematopoietic stem cell therapy. The effectiveness of this therapy requires the recruitment of transduced donor cells to the CNS. This is only found to occur after mice are conditioned with total body irradiation, due to the increase in CNS cytokine production and blood brain barrier permeability that occurs. As the use of total body irradiation in pediatric patients has been linked to future developmental problems, this myeloablation approach is often avoided in younger patients in favor of a conditioning regimen using the chemotherapy drugs, busulfan and cyclophosphamide. Whether donor cells can enter the CNS when a busulfan and cyclophosphamide conditioning regimen is used has not been determined. In this study we plan to quantify the cytokine and blood-brain barrier permeability increases necessary for donor cells to be recruited to the CNS after total body irradiation. We will then investigate whether busulfan and cyclophosphamide conditioning and/or the chronic neuroinflammation present in GM1 mice can produce similar conditions and facilitate the recruitment of donor hematopoietic stem cells to the CNS. Finally we will assess whether ex vivo hematopoietic stem cell gene therapy is still an effective therapy when busulfan and cyclophosphamide are used for myeloablative conditioning

Preventing Erectile Dysfunction after Radical Prostatectomy: Nerve-Sparing Techniques, Penile Rehabilitation, and Novel Regenerative Therapies

Erectile dysfunction is a known and much-dreaded functional consequence of radical prostatectomy. Dr. Patrick Walsh pioneered the nerve-sparing radical retropubic prostatectomy in the early 1980s, which has mitigated the morbidity of this surgery. Post-operative potency rates range widely from 20 to 80%, however, and depend on myriad factors including age, preoperative potency, and degree of nerve-sparing during surgery. Over the past four decades several developments have continued to offer hope to patients and clinicians alike, including refined understanding of cavernosal nerve neuroanatomy, beneficial modifications in surgical technique, as well as the advent of robotic surgery. Furthermore, multiple pre- and post-operative penile rehabilitation techniques using mechanotherapy and pharmaceuticals have also improved functional recovery. This paper examines erectile dysfunction as a consequence of radical prostatectomy, including the physiology of erections, the pathophysiology of post-operative erectile dysfunction, novel surgical techniques to enhance neurovascular bundle preservation, and penile rehabilitation strategies involving hyperbaric oxygen, neuroprotective pharmaceuticals, dehydrated human amnion-chorion membrane allografts, and mesenchymal stem cell therapy