A feasibility study of X‐ray phase‐contrast mammographic tomography at the Imaging and Medical beamline of the Australian Synchrotron

Results are presented of a recent experiment at the Imaging and Medical beamline of the Australian Synchrotron intended to contribute to the implementation of low‐dose high‐sensitivity three‐dimensional mammographic phase‐contrast imaging, initially at synchrotrons and subsequently in hospitals and medical imaging clinics. The effect of such imaging parameters as X‐ray energy, source size, detector resolution, sample‐to‐detector distance, scanning and data processing strategies in the case of propagation‐based phase‐contrast computed tomography (CT) have been tested, quantified, evaluated and optimized using a plastic phantom simulating relevant breast‐tissue characteristics. Analysis of the data collected using a Hamamatsu CMOS Flat Panel Sensor, with a pixel size of 100 µm, revealed the presence of propagation‐based phase contrast and demonstrated significant improvement of the quality of phase‐contrast CT imaging compared with conventional (absorption‐based) CT, at medically acceptable radiation doses.     

Mo_2C/γ-Al_2O_3催化剂上苯加氢反应的原位红外光谱研究

采用程序升温反应法制备了钝化态、还原钝化态和新鲜态Mo2C/γ-Al2O3催化剂,结合原位红外光谱表征技术和反应性能评价,考察、比较了三种催化剂苯加氢反应活性.原位红外光谱结果表明,新鲜态Mo2C/γ-Al2O3催化剂在室温就显示了较好的苯加氢反应活性,表现了类贵金属的催化活性.CO吸附在反应前后新鲜态Mo2C/γ-Al2O3催化剂上的对比结果表明,低价态的Mo位(Moδ+(0δ2))是苯加氢反应活性中心.三种催化剂的反应活性结果表明,新鲜态Mo2C/γ-Al2O3催化剂反应活性最好,催化剂寿命最长,失活之后在500°C下H2处理即可恢复原有活性.     

Radiophotolumenescence of Irradiated Polymethylmethacrylate Doped with Some Charge Transfer Complexes

Radiophotolumenescence (RPL) of irradiated and non irradiated thin films of polymethylmethacrylate (PMMA) doped with anthracene (Anth) as a donor, and tetracyanoquinodimethane (TCNQ) as an acceptor, has been investigated. The RPL – glow spectrum was recorded to study the characterizing emission bands from the point of view of glow peak position and intensity and hence the prospective relative sensitivities. RFL – signal fading after one month storage in dark at room temperature post gamma irradiation was also studied. PMMA doped with 6:4 donor to acceptor ratio has been proved to be the most sensitive one with less fading regarding gamma detection. On the other hand 2 Anth: 8 TCNQ was found to be the proper dopant concentration ratio for thermal neutron detection.     

The credit risk+ model with general sector correlations

We consider an enhancement of the credit risk⁺ model to incorporate correlations between sectors. We model the sector default rates as linear combinations of a common set of independent variables that represent macro-economic variables or risk factors. We also derive the formula for exact VaR contributions at the obligor level.     

Zur Methodik der Messung der Aktivität von umschlossenen γ-Strahlungsquellen mittels Ionisationskammern

In der Arbeit wird über eine Empfehlung zur Methodik der Weitergabe der Aktivitätseinheit für umschlossene γ-Strahlungsquellen von den Normalen der metrologischen Slaatsämter der UdSSR (WNIIM) und der DDR (ASMW) an Normale niederer Ordnung berichtet. Die Weitergabe der Aktivitätseinheit geschieht durch Vergleich mittels Ionisationskammern. Die Empfehlung bezieht sich auch auf solche Fälle, in denen neben dem Hauptnuklid ein Verunreinigungsnuklid in der Quelle enthalten ist, sowie auf solche, bei denen unterschiedlicher Aufbau der zu vergleichenden Quellen vorliegt. Auβerdem umfaβt die Empfehlung die Methode der Fehlerrechnung.     

Hydrothermal formation of tobermorite studied by in situ X‐ray diffraction under autoclave condition

Hydrothermal formation of tobermorite from a pre‐cured cake has been investigated by transmission X‐ray diffraction (XRD) using high‐energy X‐rays from a synchrotron radiation source in combination with a newly designed autoclave cell. The autoclave cell has a large and thin beryllium window for wide‐angle X‐ray diffraction; nevertheless, it withstands a steam pressure of more than 1.2 MPa, which enables in situ XRD measurements in a temperature range of 373 to 463 K under a saturated steam pressure. Formation and/or decomposition of several components has been successfully observed during 7.5 h of reaction time. From the intensity changes of the intermediate materials, namely non‐crystalline C–S–H and hydroxylellestadite, two pathways for tobermorite formation have been confirmed. Thus, the newly developed autoclave cell can be used for the analyses of reaction mechanisms under specific atmospheres and temperatures.     

MiniMax: What has been learned thus far

Summary A small experiment, ?MiniMax?, has been set up in the C0 intersection region of the Fermilab Tevatron to seek evidence for disoriented chiral condensates and to study other forward physics phenomena. The experiment consists of a proportional wire chamber telescope accompanied by scintillation (trigger) counters, a lead converter, and followed by an electromagnetic calorimeter. The solid angle accepted is a cone centered at pseudorapidity (η) of 4.1 and of radius (in η-ϕ space) of about 0.6. Over 2.5 million events thus far have demonstrated the successful operation of the apparatus, however to date the analysis has not progressed sufficiently to permit any conclusions concerning disoriented chiral condensates. presented byL. W. Jones Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Tracking of flare-generated interplanetary shock waves, responsible for Forbush decreases, by observing type-II radio bursts

Summary New possibilities are pointed out of a more accurate identification of solar flares, responsible for Forbush decreases of galactic cosmic rays, caused by flare-generated interplanetary shock waves, based on tracking type-II radio bursts. Nine solar flares, observed between September 1978 and December 1979, generated shock waves which produced intensive type-II radio bursts observed in the hectometric and kilometric wave range by the ISEE-3 satellite. All the type-II shocks were responsible for Forbush decreases. Since the observation of type-II radio bursts enables us to follow the propagation of shock waves practically from the place where they are generated deep in the solar corona, through interplanetary space as far as the Earth, these observations provide the possibility of exact identification of Forbush decreases with the corresponding flares. These observations have also supplied a further dimension for analysing interplanetary disturbances and forecasting Forbush decreases.

---

Riassunto Sono messe in evidenza nuove possibilità per una piú accurata identificazione dei brillamenti solari responsabili delle diminuzioni di Forbush, nell’intensità dei raggi cosmici galattici, dovute ad onde d’urto interplanetarie. Tali possibilità sono basate sull’osservazione dello sviluppo spazio-temporale delle sorgenti della radioemissione di tipo II. Durante il periodo settembre 1978-dicembre 1979, sono stati osservati nove brillamenti solari, che generavano onde d’urto producenti un’intensa radioemissione di tipo II osservata dal satellite ISEE-3 nell’intervallo di lunghezze d’onda ettometrico e chilometrico. Tutte queste onde d’urto erano responsabili delle diminuzioni di Forbush. Poiché l’osservazione della radioemissione di tipo II ci permette di seguire la propagazione delle onde d’urto praticamente dal posto dove loro sono generate, in profondità nella corona, fin nello spazio interplanetario verso la Terra, i risultati ottenuti forniscono la possibilità di una precisa identificazione della connessione tra le diminuzioni di Forbush ed i brillamenti corrispondenti. Queste osservazioni danno anche un ulteriore contributo all’analisi delle perturbazioni interplanetarie ed alla possibilità di previsione di diminuzioni di Forbush.

---

Резюме Указываются новые возможности, связанные с прослеживанием радиовспышек типа II, для более точной идентификации солнечных вспышек, ответственных за убывание Форбуша, которые вызывают межпланетные ударные волны. Девять солнечных вспышек, наблюдавшися между сентябрем 1978 и декабрем 1979, образовали ударные волны, которые вызвали интенсивные радио-вспышки типа II, которые наблюдались спутником ISEE-3. Все эти ударные волны типа II ответственны за убывания Форбуша. Так как навпюдения радио-вспышек типа II позволяет нам проследить распространение ударных волн практически от места их образования глубоко в солнечной короне через межпланетное пространство до Земли, то такие наблюдения обеспечивают возможность точной идентификации убываний Форбуша в зависимости от соответствующих солнечных вспышек. Эти наблюдения также позволяют анализировать межпланетные возмущения и предсказывать убывания Форбуша.

     

Algebraic independence of the periods of abelian integrals

Abelian integrals of the first and the second kind are proved to have two algebraically independent periods. Some corollaries concerning the algebraic independence of the values of Euler's beta and gamma functions at rational points are derived.Translated fromMatematicheskie Zametki, Vol. 60, No. 5, pp. 681–691, November, 1996.