104 research outputs found
Feynman motives
No full textThis book presents recent and ongoing research work aimed at understanding the mysterious relation between the computations of Feynman integrals in perturbative quantum field theory and the theory of motives of algebraic varieties and their periods. One of the main questions in the field is understanding when the residues of Feynman integrals in perturbative quantum field theory evaluate to periods of mixed Tate motives. The question originates from the occurrence of multiple zeta values in Feynman integrals calculations observed by Broadhurst and Kreimer.
Two different approaches to the subject are described. The first, a “bottom-up” approach, constructs explicit algebraic varieties and periods from Feynman graphs and parametric Feynman integrals. This approach, which grew out of work of Bloch–Esnault–Kreimer and was more recently developed in joint work of Paolo Aluffi and the author, leads to algebro-geometric and motivic versions of the Feynman rules of quantum field theory and concentrates on explicit constructions of motives and classes in the Grothendieck ring of varieties associated to Feynman integrals. While the varieties obtained in this way can be arbitrarily complicated as motives, the part of the cohomology that is involved in the Feynman integral computation might still be of the special mixed Tate kind. A second, “top-down” approach to the problem, developed in the work of Alain Connes and the author, consists of comparing a Tannakian category constructed out of the data of renormalization of perturbative scalar field theories, obtained in the form of a Riemann–Hilbert correspondence, with Tannakian categories of mixed Tate motives. The book draws connections between these two approaches and gives an overview of other ongoing directions of research in the field, outlining the many connections of perturbative quantum field theory and renormalization to motives, singularity theory, Hodge structures, arithmetic geometry, supermanifolds, algebraic and non-commutative geometry.
The text is aimed at researchers in mathematical physics, high energy physics, number theory and algebraic geometry. Partly based on lecture notes for a graduate course given by the author at Caltech in the fall of 2008, it can also be used by graduate students interested in working in this area
First-year experience with MICA technique: learning difficulties, mistakes, and results
No full textBACKGROUND: Hallux valgus is a very common forefoot disorder, first named by Carl Hueter (1871) as a condition with a static subluxation of the first metatarsophalangeal joint with lateral deviation of the great toe and medial deviation of the first metatarsal. It usually leads to pain and functional impairment of the foot. With the continuous evolution of technology and the idea to shift open Austin Akin osteotomy to MIS surgery, more recently Redfern and Vernois developed the Minimally Invasive Chevron Akin (MICA) technique. The use of this technique has been vastly studied by the authors, but to our knowledge there is a scarce literature production by independent authors reporting their experience in the use of this technique. The aim of the present study was to show our preliminary results in the use of MICA technique performed by the same surgeon during his first year of use, underlining the learning difficulties, mistakes and results achieved during this frame of time. METHODS: The MICA procedure was performed on 60 feet from July 2018 to July 2019. A follow-up of at least 11 months was achieved. The clinical outcome was measured through AOFAS Score. RESULTS: The mean patients age was 51.5 years old (range: from 36 to 72 years old). The mean AOFAS Score was 90.4, interestingly 24 patients (40% of the total of 60 patients) had AOFAS Score set over 90. CONCLUSIONS: MICA osteotomy marries percutaneous surgery with the Austin Akin osteotomy, that have been and are widely used for the treatment of hallux valgus. It is possible to achieve the good results of a well know surgery with a stable fixation and obtain all the goals of percutaneous surgery, such has limited pain, good postoperative range of motion and an overall positive experience of the patient. The learning curve, if the surgeon is correctly instructed, is steep, but the results are good since the first procedures. On the other hand, the complications/surgical errors reported are limited, easily resolvable and do not impact the overall positive results. (Cite this article as: Marcolli D, Pichierri I, Minoli C, Mazzotti A, Compagnoni R, Randelli PS. First-year experience with MICA technique: learning difficulties, mistakes, and results. Minerva Orthop 2024;75:7-13. DOI: 10.23736/S2784-8469.23.04330-4
Management of distal radius fractures: treatment protocol and functional results.
No full textDistal radius fractures are the most frequent lesions encountered during clinical practice. The treatment is controversial and still debated in the literature. For a correct management of these lesions many authors recently emphasised the importance of anatomical reduction, a stable fixation and early joint mobilisation. We report our experience in the daily management of these lesions. The fractures are evaluated considering fracture type, fracture reduction criteria, adequacy of reduction criteria and overall fracture stability. The best treatment option must be decided in accordance to the type of fracture, the extent of metaphyseal comminution, the quality of the bone and the medical condition of the patient
Do atmospheric aerosols form glasses?
No full textZobrist B, Marcolli C, Pedernera DA, Koop T. Do atmospheric aerosols form glasses? ATMOSPHERIC CHEMISTRY AND PHYSICS. 2008;8(17):5221-5244.A new process is presented by which water soluble organics might influence ice nucleation, ice growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when a liquid is cooled without crystallization until the viscosity increases exponentially and molecular diffusion practically ceases. The glass transition temperatures, Tg, homogeneous ice nucleation temperatures, Thom, and ice melting temperatures, Tm, of various aqueous inorganic, organic and multi-component solutions are investigated with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose, raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulfate and mixtures of dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulfate (M5AS), of two polyols, of glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous solutions of the investigated inorganic solutes show Tg values that are too low to be of atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form glasses at low but atmospherically relevant temperatures (≤230 K). To apply the laboratory data to the atmospheric situation, the measured phase transition temperatures were transformed from a concentration to a water activity scale by extrapolating water activities determined between 252 K and 313 K to lower temperatures. The obtained state diagrams reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher Tg of their respective solutions at a given water activity. To a lesser extent, Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol particles containing larger (≳150 g mol−1) and more hydrophobic organic molecules are more likely to form glasses at intermediate to high relative humidities in the upper troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be significantly impeded or even completely inhibited in organic-enriched aerosols at upper tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric relative humidity
Oxalic acid as a heterogeneous ice nucleus in the upper troposphere and its indirect aerosol effect
No full textZobrist B, Marcolli C, Koop T, et al. Oxalic acid as a heterogeneous ice nucleus in the upper troposphere and its indirect aerosol effect. ATMOSPHERIC CHEMISTRY AND PHYSICS. 2006;6(10):3115-3129.Heterogeneous ice freezing points of aqueous solutions containing various immersed solid dicarboxylic acids (oxalic, adipic, succinic, phthalic and fumaric) have been measured with a differential scanning calorimeter. The results show that only the dihydrate of oxalic acid (OAD) acts as a heterogeneous ice nucleus, with an increase in freezing temperature between 2 and 5 K depending on solution composition. In several field campaigns, oxalic acid enriched particles have been detected in the upper troposphere with single particle aerosol mass spectrometry. Simulations with a microphysical box model indicate that the presence of OAD may reduce the ice particle number density in cirrus clouds by up to ~50% when compared to exclusively homogeneous cirrus formation without OAD. Using the ECHAM4 climate model we estimate the global net radiative effect caused by this heterogeneous freezing to result in a cooling as high as −0.3 Wm−2
Fracture of a polyethylene post in a 9-year-old posterior-stabilized knee prosthesis: light microscopy and SEM evaluation
No full textObjective Aim of this study is to evaluate the surface of the TKA polyethylene liner, harvested after the breakage of the post nine years after the implant in a 63 years old female (BMI 39) after an hyperextension trauma.
Methods During the revision we harvested sample of the periprosthetic tissue which was prepared for the light microscopy evaluation. The samples were stained using both haematoxylineosin and Von Kossa. The PE liner was prepared for the Scanning Electron Microscopy.
Results The SEM evaluation revealed two different damage patterns considering the medial part and the lateral aspect of the sample. The medial part presented a fracture line laminated in front and smooth behind and with the tear lines with a medio-lateral and anterior posterior orientation. The lateral part presented a sharp fracture line that ends anteriorly with a laminated tear paralleled to the anterior edge of the polyethylene insert, and which implies that this area could be the terminal failure area of the fractured post. The medial part of the fracture edge appears to be smooth and with a different orientation of the fracture lines.
Conclusions These features could be explained with a ‘‘two stage’’ rupture of the polyethylene post. This could have been caused by a non-optimal ligamentous balance that weakened the post, which was finally broken by a postero-anterior stress
Indications, Associated Procedures, and Results of Ankle Plafond-Plasty for Varus Ankle Osteoarthritis: A Systematic Review and Meta-Analysis
No full textBackgrounds: Plafond-plasty is a joint-preserving procedure to treat varus ankle osteoarthritis (OA) with asymmetrical joint involvement. The aim of this systematic review and meta-analysis was to evaluate indications, different surgical techniques, associated procedures, and results of plafond-plasty in varus ankle OA and to analyze the level of evidence (LOE) and quality of evidence (QOE) of the included studies. Methods: A systematic review of the literature was performed using MEDLINE, Embase, and Cochrane. Results: Five studies evaluating 99 ankles were included. A non-rigid varus ankle deformity and an ankle OA Takakura stage 3b or less were the most recommended pre-operative indications. Meta-analysis showed a significant post-operative improvement in clinical and radiological parameters. Many associated surgical procedures have been reported, the most frequent being medial additional supramalleolar osteotomy and lateral ankle ligament reconstruction. The level of evidence and methodological quality assessment of the included studies showed an overall low quality. Conclusion: Plafond-plasty seems to be a promising surgical option when managing varus ankle OA with asymmetrical joint involvement, extending the indications for joint sparing surgery. Additional associated procedures should be carefully evaluated case-by-case. Levels of Evidence: IV
Multiplicative Renormalization and Hopf Algebras
No full textContains fulltext :
84013.pdf (Author’s version preprint ) (Open Access
- …
