The geometric algebra of Fierz identities in arbitrary dimensions and signatures

We use geometric algebra techniques to give a synthetic and computationally efficient approach to Fierz identities in arbitrary dimensions and signatures, thus generalizing previous work. Our approach leads to a formulation which displays the underlying real, complex or quaternionic structure in an explicit and conceptually clear manner and is amenable to implementation in various symbolic computation systems. We illustrate our methods and results with a few examples which display the basic features of the three classes of pin representations governing the structure of such identities in various dimensions and signatures.Comment: 77 pages; version published in JHEP in 201

Approximating Mexican highways with slime mould

Plasmodium of Physarum polycephalum is a single cell visible by unaided eye. During its foraging behavior the cell spans spatially distributed sources of nutrients with a protoplasmic network. Geometrical structure of the protoplasmic networks allows the plasmodium to optimize transport of nutrients between remote parts of its body. Assuming major Mexican cities are sources of nutrients how much structure of Physarum protoplasmic network correspond to structure of Mexican Federal highway network? To find an answer undertook a series of laboratory experiments with living Physarum polycephalum. We represent geographical locations of major cities by oat flakes, place a piece of plasmodium in Mexico city area, record the plasmodium's foraging behavior and extract topology of nutrient transport networks. Results of our experiments show that the protoplasmic network formed by Physarum is isomorphic, subject to limitations imposed, to a network of principle highways. Ideas and results of the paper may contribute towards future developments in bio-inspired road planning

Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer

We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.Comment: 18 pages, 9 Figures, 4 Tables, 44 Reference

Proton G_E/G_M from beam-target asymmetry

The ratio of the proton's electric to magnetic form factor, G_E/G_M, can be extracted in elastic electron-proton scattering by measuring either cross sections, beam-target asymmetry or recoil polarization. Separate determinations of G_E/G_M by cross sections and recoil polarization observables disagree for Q^2 > 1 (GeV/c)^2. Measurement by a third technique might uncover an unknown systematic error in either of the previous measurements. The beam-target asymmetry has been measured for elastic electron-proton scattering at Q^2 = 1.51 (GeV/c)^2 for target spin orientation aligned perpendicular to the beam momentum direction. This is the largest Q^2 at which G_E/G_M has been determined by a beam-target asymmetry experiment. The result, \muG_E/G_M = 0.884 +/- 0.027 +/- 0.029, is compared to previous world data.Comment: 8 pages, 6 figures, Updated to be version published in Physical Review

Measurement of the Electric Form Factor of the Neutron at Q^2=0.5 and 1.0 (GeV/c)^2

The electric form factor of the neutron was determined from measurements of the \vec{d}(\vec{e},e' n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle detector. We find G_E^n = 0.0526 +/- 0.0033 (stat) +/- 0.0026 (sys) and 0.0454 +/- 0.0054 +/- 0.0037 at Q^2 = 0.5 and 1.0 (GeV/c)^2, respectively.Comment: 5 pages, 2 figures, as publishe

Majorana: from atomic and molecular, to nuclear physics

In the centennial of Ettore Majorana's birth (1906-1938?), we re-examine some aspects of his fundamental scientific production in atomic and molecular physics, including a not well known short communication. There, Majorana critically discusses Fermi's solution of the celebrated Thomas-Fermi equation for electron screening in atoms and positive ions. We argue that some of Majorana's seminal contributions in molecular physics already prelude to the idea of exchange interactions (or Heisenberg-Majorana forces) in his later workson theoretical nuclear physics. In all his papers, he tended to emphasize the symmetries at the basis of a physical problem, as well as the limitations, rather than the advantages, of the approximations of the method employed.Comment: to appear in Found. Phy

Low Q^2 measurements of the proton form factor ratio mupGE/GMmu_p G_E / G_M

We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis.Comment: 12 pages, 5 figures, archival paper for proton form factor extraction from Jefferson Lab "LEDEX" experimen

Ultrasonografia cu substanţă de contrast în examinarea tumorilor renale. Comparaţie între un caz de oncocitom şi un caz de cancer cu celule renale şi studiu aprofundat al literaturii

Universitatea de Medicină şi Farmacie Iuliu Haţieganu, Cluj-NapocaIntroducere. Oncocitomul renal (OCR) reprezintă o tumoră benignă, a cărui diagnostic este în mod frecvent incidental. Cancerul cu celule renale (CCR) este cea mai frecventă patologie malignă renală. Ultrasonografia este în mod frecvent prima linie de evaluare a acestor formaţiuni, studiul fiind completat cu examinarea prin tomografie computerizată cu substanţă de contrast (CECT). Studiul prezintă două cazuri – OCR și, respectiv, CCR. Printr-o amplă consultare a literaturii de specialitate, corelată cu experienţa de până în prezent, se dorește identificarea aportului ultrasonografiei cu substanţă de contrast (CEUS) în diagnosticul tumorilor renale. Materiale și metodă. Ambii pacienţi au fost de sex feminin, vârsta fiind de 35 și, respectiv, 53 de ani. Evaluarea imagistică a inclus, în ambele cazuri, ecografia în mod B, Doppler color, pulsat, precum și cu substanţă de contrast (SC) (Sonovue-Bracco, Italia, 1,6 ml intravenos în bolus). Caracteristicile captării și spălării agentului de contrast au fost evaluate folosind un program dedicat (Sonoliver, Tomtec Imaging Systems). S-au calculat pentru fiecare formaţiune și pentru parenchimul martor următorii indici: Time to peak (TTp), intensitatea maximă (IMAX), timpul de spălare (RT), timpul mediu de tranzit (mTT). Investigaţiile au fost completate prin CECT. Rezultate. Examinarea ultrasonografică a primei paciente a identificat o masă localizată la nivelul corticalei rinichiului drept, hiperecogenă comparativ cu aceasta, omogenă, bine delimitată. Formaţiunea măsura 30/31/31 mm. Examinările Doppler color și pulsat au relevat vascularizaţie periferică și centrală, ce îmbrăca aspectul de ,,spiţe de roată”. La introducerea substanţei de contrast, periferia tumorii a prezentat captare intensă. IMAX atribuită formaţiunii a fost inferioară parenchimului normal (92,2% vs 100%). Valorile RT, TTp și mTT au fost superioare corticalei de referinţă (8,44s vs 6,01s; 17,59s vs 15,7s; 20,19s vs 16,97s). Centrul formaţiunii a captat mai lent SC, rămânând hipocaptant. Formaţiunea corticală stângă, identificată la cea de-a doua pacientă, a fost inomogenă și relativ hipercogenă, comparativ cu parenchimul normal. Delimitarea tumorii, raportată la cazul precedent, nu a fost la fel de netă. Dimensiunile au fost de 32/28,7/27 mm. Examinările Doppler color și pulsat au identificat vascularizaţie bogată peritumorală. Post-CEUS, la nivelul tumorii și a corticalei de referinţă s-au calculat IMAX (84,95% vs 100%; ), RT (14,87s vs 16,6s), TTp (16,96s vs 18,25s), mTT (49,41s vs 69,85s). Examinarea CECT a primului caz consolidează diagnosticul de oncocitom, iar la cel de-al doilea – diagnosticul de CCR. Rezultatul anatomopatologic al pieselor de rezecţie identifică leziunile ca OCR și CCR. Discuţii. Procesele de neovascularizaţie imprimă tumorilor renale o comportare aparte faţă de corticala indemnă. În cazurile prezentate, indicii CEUS măsuraţi pentru OCR și CCR sunt sensibil diferiţi atât între ei, cât și faţă de cei ai parenchimului normal. Literatura de specialitate subliniază nevoia unor studii ample, concentrate asupra diagnosticului tumorilor renale prin intermediul CEUS. Concluzii. Abilitatea CEUS de a detecta fluxuri lente, capacitatea de cuantificare în timp real și posibilităţile de postprocesare pot fi considerate argumente ce susţin validitatea metodei în cuantificarea tumorilor renale. Constrângeri în cazul pacienţilor cu insuficienţă renală practic nu există. Cuantificarea curbelor de spălare în cadrul unui lot semnificativ de pacienţi ar putea identifica parametrii specifici OCR și CCR

The Proton Elastic Form Factor Ratio at Low Momentum Transfer

High precision measurements of the proton elastic form factor ratio have been made at four-momentum transfers, Q^2, between 0.2 and 0.5 GeV^2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q^2 range the deviation from unity is primarily due to GEp being smaller than the dipole parameterization.Comment: 5 pages, 2 figure