[en] The transient response of two-level atoms to bichromatic optical field excitation is studied both theoretically and experimentally. The bichromatic optical field consists of a strong pump frequency component and a relatively weak perturber frequency component. Both pump and perturber fields are near-resonant with the atomic transition. Theoretical investigation covers the atomic dynamics under wide-ranging bichromatic excitation conditions. It is shown that the atomic dynamics is very complex. Generally speaking, the strong pump field tends to stabilize the atoms against the influence of the perturber field. Exceptions occur when the perturber field is detuned from the pump field by the Rabi frequency of the pump or its subharmonics. In addition, it is found that the atomic evolution is sensitive to the initial relative phase of the pump and perturber field. An experiment has been performed using a ¹⁷⁴Yb atomic beam. The bichromatic field is in the strong-pump-weak-perturber regime, where the pump field is always resonant with the ¹⁷⁴Yb atomic transition. Optical mutation of a dressed-atom transition is observed for the first time. Also, dressed-state polarization of initially ground-state atoms is realized when the perturber field is detuned from the atomic transition by the Rabi frequency of the pump and the two excitation fields have some specific initial relative phase. In both cases, the experimental results are in good agreement with the predictions of the theory

[en] Using various ground observations at South Pole, Antarctica (invariant magnetic latitude -74 degree) and its conjugate point, Frobisher Bay, Canada, the author has studied the following aspects of nightside polar cap auroral activity: the appearance and disappearance of polar cap auroras (diffuse and discrete) associated with substorms and interplanetary magnetic field (IMF) variations; auroral optical emission line intensities; and the seasonal variation of auroral conjugacy. The observations show that the polar cap auroras usually fade away before the expansive phase of a substorm and bright auroral arcs reach high latitude (-74 degree) near the recovery phase. Just before the auroras fade away the discrete polar cap auroral arcs, which are usually on the poleward boundary of the diffuse aurora, intensify for 1 to 2 minutes. The observations also indicate the IMF may have stronger control over polar cap auroral activity than do substorms. A search for energy spectral variation of precipitating electrons using the intensities of 630.0 nm (0) and 427 nm (N₂⁺) auroral emission lines reveals no dramatic changes in the energy spectrum; instead, the data show possible atmospheric scattering and geometric effects on the photometric measurements while the bright auroral arc is moving into the polar cap. The conjugate observations show that the stormtime auroral electrojet current, which is associated with the bright auroral arc, in most cases reaches higher (lower) latitudes in the winter (summer) hemisphere. An asymmetric plasma sheet (with respect to the neutral sheet) is proposed, which expands deeper into the winter lobe, under a tilted geomagnetic dipole. Accordingly, the winter polar cap would have smaller area and the auroral electrojet would be at higher latitude

[en] We experimentally investigate the transient dynamics of two-level atoms under bichromatic optical excitation. Novel new dynamical behavior is observed that may be interpreted classically in terms of the vector model or in a modem vein as resonant monochromatic excitation of dressed atoms. We show the first observation of dressed-atom optical mutations. We also show that the system dynamics depend critically on the initial relative phase of the two excitation-field components and that controlled bichromatic excitation may lead to complete dressed-state polarization of initially ground-state atoms

[en] The 56MHz Superconducting RF (SRF) cavity for RHIC places high demands High Order Mode (HOM) damping, as well as requiring a high field at gap with fundamental mode frequency. The damper of 56MHz cavity is designed to extract all modes to the resistance load outside, including the fundamental mode. Therefore, the circuit must incorporate a high-pass filter to reflect back the fundamental mode into the cavity. In this paper, we show the good frequency response map obtained from our filter's design. We extract a circuit diagram from the microwave elements that simulate well the frequency spectrum of the finalized filter. We also demonstrate that the power dissipation on the filter over its frequency range is small enough for cryogenic cooling.

[en] A 56 MHz superconducting RF cavity was designed for a luminosity upgrade of the Relativistic Heavy Ion Collider (RHIC), including requirements for Higher Order Mode (HOM) damping. In this paper, we describe our optimization of the damper's performance, and modifications made to its original design. We also show the effects of the damper geometry on the cavity's HOM impedance. To reduce the likelihood of magnetic breakdown, we lowered the magnetic field enhancement at the ports to a value less than the highest field in the cavity. We simulated all monopole and dipole HOMs up to 1GHz with their frequencies, mode configurations, R/Qs, and shunt impedances, verifying that all modes are well-damped with the optimized design and configuration. The 56 MHz superconducting RF cavity is a quarterwave resonator designed to have a gap voltage of 2.5 MV. Our plans are to place this beam-driven resonator at a common section of RHIC to provide a storage RF potential for both rings. The large bucket of the cavity will reduce spill due to Intra-Beam Scattering (IBS), and thus increase the luminosity for the detectors. It is very important to damp all the cavity's Higher Order Modes (HOMs) to avoid beam instabilities. The design chosen for the HOM damper is a magnetically coupled loop located at the rear end of the cavity. The loop and its port geometry must be optimized to assure sufficient damping, avoid a large enhancement of the local magnetic field. A high-pass filter is included in the circuit to reduce the power extraction from the fundamental mode. The number of HOM dampers used and their configuration also are important factors for the damping and cooling system. A small loop area will couple out less power from the cavity's fundamental mode, thus reducing the voltage and power dissipation in the damper's filter circuit; however, it might not be sufficient for HOM damping. This problem is resolved by increasing the number of the HOM dampers and carefully choosing their location. Details of the high-pass filter will be discussed in another paper.

[en] Earlier, we reported that a 56 MHz cavity was designed for a luminosity upgrade of the RHIC, and presented the requirements for Higher Order Mode (HOM) damping, the design of the HOM dampers, along with measurements and simulations of the HOM dampers. In this report, we describe our optimization of the dampers performance, and the modifications we made to their original design. We also optimized the number of the HOM dampers, and tested different configurations of locations for them.

No abstract available

[en] To evaluate the prognostic value of ¹⁸ F-FDG positron emission tomography (PET) in patients (pts) with coronary artery disease (CAD) and left ventricular dysfunction and to establish whether myocardial revascularization (RVS) will decrease the cardiac events in pts with perfusion-metabolism mismatch. 107 consecutive pts (mean age 57±9 yr) with CAD and left ejection fraction (LVEF=38±9%) who underwent ¹'8F-FDG PET imaging and ^99mTc-MIBI SPECT imaging were followed up for 24 ± 5 mons. Myocardial segments were classified as perfusion-metabolism mismatch (MM) and Match (M). LVEF and left ventricular end diastolic diameter (LVEDD) were measured with echocardiography (Echo). Fifty-nine pts underwent Echo, respectively. Cardiac death, myocardial infarction (MI), unstable angina pectoris and late RVS (>3 mon) were considered cardiac events. Among 64 patients with 2 or more MM segments, 35 pts received RVS (MM1) and 29 pts received medical therapy (MM2). Among 43 pts with less than 2 MM segment, 24 pts underwent RVS (M1) and 19 pts underwent medical therapy (M2). After RVS, LVEF in MM1 was increased from 38±8% to 48±10% (p<0.0001) in POS1 and to 52±10% (P<0.001) in POS2. LVEDD in MM1 was decreased form 62±8 mm to 53±7 mm (p<0.0001) in POS1 and to 53±8 mm (P<0.01) in POS2. However, LVEF and LVEDD were unchanged in M1 after RVS (P>0.05). The cardiac event rate of 51.7% (15/29) in MM2 was significantly higher than that of 2.9% (1/35) in MM1 (x²=20.1, p<0.0001), higher that of 16.7 %(3/24) in M1 (x²=7.02, P=0.002) and that of 21.1% in M2(x²=4.5, P=0.03). The results suggest that the presence of MM in pts with CAD and left ventricular dysfunction is associated with poor prognosis with medical therapy, and these pts may need aggressive RVS to prevent a future cardiac event and to improve left ventricular function

[en] Purpose: To replace the paper records, we designed an electronic records function for plan checked meeting in our in-house developed radiotherapy information management system(RTIMS). Methods: Since 2007, the RTIMS has been developed on a database and web service of Apache+PHP+MySQL, and almost all computers and smartphones could access the RTIMS through IE browser, to input, search, count, and print the data. In 2012, we also established an radiation therapy case conference multi-media system(RTCCMMS) based on Windows Remote Desktop feature. Since 2013, we have carried out the treatment plan checked meeting of the physics division in every afternoon for about half an hour. In 2014, we designed an electronic records function, which includes a meeting information record and a checked plan record. And the meeting record includes the following items: meeting date, name, place, length, status, attendee, content, etc. The plan record includes the followings: meeting date, meeting name, patient ID, gender, age, patient name, course, plan, purpose, position, technique, CTsim type, plan type, primary doctor, other doctor, primary physicist, other physicist, difficulty, quality, score, opinion, status, note, etc. Results: In the past year, the electronic meeting records function has been successfully developed and implemented in the division, and it could be accessed from an smartphone. Almost all items have the corresponding pull-down menu selection, and each option would try to intelligently inherit default value from the former record or other form. According to the items, we could do big data mining to the input data. It also has both Chinese and English two versions. Conclusion: It was demonstrated to be user-friendly and was proven to significantly improve the clinical efficiency and quality of treatment plan. Since the RTIMS is an in-house developed system, more functions can be added or modified to further enhance its potentials in research and clinical practice. Project supported by the National Natural Science Foundation of China (Grant No.81101694)

[en] Purpose: To study quality assurance (QA) of volumetric modulated arc therapy (VMAT) after the 6MV and 10MV photon beam source modeling, referring to the Varian TrueBeam representative beam data for Eclipse. Methods: The source model needs specific measured beam data, such as PDDs and profiles, diagonal profile, output factors (OFs), and MLC transmission factor (TF) and dosimetric leaf gap (DLG), et al. We downloaded the representative data from myVarian website, which includes TrueBeam 4MV-15MV photon beam data and 6MeV-22MeV electron beam data in w2CAD file format for use with Eclipse and in Excel spreadsheet format for use in data comparison. The beam data in W2CAD format can be imported into the Eclipse system and calibrated for use, as appropriate. We used PTW MP3 water tank to measure the beam data in some typical field sizes, and compared the measured data with the representative data. We found that the PDDs, profiles and OFs are similar. However according to some papers and our measurements, we decided that our MLC TF and DLG are 1.58 and 1.33 (6MV), 1.79 and 1.57 (10MV), respectively. After we had configured the anisotropic analytical algorithm (AAA) with the representative data in Eclipse, we also have done dosimetric verification for 88 VMAT plans. Results: The end-to-end test procedures of VMAT were performed for 6MV and 10MV energy modes. The NE Farmer ion chamber mean measurements showed 1.2% (6MV, 38 cases) and 1.2% (10MV, 50 cases) between measurement and calculation; the Sun Nuclear ArcCheck mean measurements demonstrated gamma pass rates are as followings: 98.9%, 93.2%, 61.0% for 6MV, and 98.9%, 91.9%, 59.5% for 10MV, using 3%/3mm, 2%/2mm, 1%/1mm, 10% threshold criteria, respectively. Conclusion: The representative data is applicable to our TrueBeam for the VMAT plan, though our MLC factors are a little different, and its patientspecific QA is good.