Suppression of stimulated Brillouin and Raman scatterings using an alternating frequency laser and transverse magnetic fields

A novel scheme to suppress both stimulated Brillouin scattering(SBS) and stimulated Raman scattering(SRS) by combining an alternating frequency(AF) laser and a transverse magnetic field is proposed. The AF laser allows the laser frequency to change discretely and alternately over time. The suppression of SBS is significant as long as the AF difference is greater than the linear growth rate of SBS or the alternating time of the laser frequency is shorter than the linear growth time of SBS. However, the AF laser proves ineffective in suppressing SRS, which usually has a much higher linear growth rate than SBS. To remedy that, a transverse magnetic field is included to suppress the SRS instability. The electrons trapped in the electron plasma waves(EPWs) of SRS can be accelerated by the surfatron mechanism in a transverse magnetic field and eventually detrapped. While continuously extracting energy from EPWs, the EPWs are dissipated and the kinetic inflation of SRS is suppressed. The one-dimensional particle-in-cell simulation results show that both SBS and SRS can be effectively suppressed by combining the AF laser with a transverse magnetic field with tens of Tesla. The total reflectivity can be dramatically reduced by more than one order of magnitude. These results provide a potential reference for controlling SBS and SRS under the related parameters of inertial confinement fusion.

Solitary fibrous tumors in abdomen and pelvis:Imaging characteristics and radiologic-pathologic correlation

AIM:To describe the imaging features of solitary fibrous tumors(SFTs)in the abdomen and pelvis,and the clinical and pathologic correlations.METHODS:Fifteen patients with pathologically confirmed SFTs in the abdomen and pelvis were retrospectively studied with imaging techniques by two radiologists in consensus.Patients underwent unenhanced and contrast-enhanced imaging,as follows:3 with computed tomography(CT)and magnetic resonance imaging(MRI)examination,8 with CT examination only,and 4 with MRI examination only.Image characteristics such as size,shape,margin,attenuation or intensity,and pattern of enhancement were analyzed and correlated with the microscopic findings identified from surgical specimens.In addition,patient demographics,presentation,and outcomes were recorded.RESULTS:Of the 15 patients evaluated,local symptoms related to the mass were found in 11 cases at admission.The size of the mass ranged from 3.4 to 25.1cm(mean,11.5 cm).Nine cases were round or oval,6were lobulated,and 10 displaced adjacent organs.Unenhanced CT revealed a heterogeneous isodense mass in 7 cases,homogeneous isodense mass in 3 cases,and punctuated calcification in one case.On MRI,most of the lesions(6/7)were heterogeneous isointense and heterogeneous hyperintense on T1-weighted images and T2-weighted images,respectively.All tumors showed moderate to marked enhancement.Heterogeneous enhancement was revealed in 11 lesions,and 7of these had cysts,necrosis,or hemorrhage.Early nonuniform enhancement with a radial area that proved to be a fibrous component was observed in 4 lesions,which showed progressive enhancement in the venous and delayed phase.No statistical difference in the imaging findings was observed between the histologically benign and malignant lesions.Three patients had local recurrence or metastasis at follow-up.CONCLUSION:Abdominal and pelvic SFTs commonly appeared as large,solid,well-defined,hypervascular masses with variable degrees of necrosis or cystic change that often displaced adjacent structures.