No abstract

No abstract

No abstract

We report experimental measurements of a high brightness electron beam produced by a ferroelectric cathode. The experiments were carried out with a cathode of area 3.7 cm2; up to 36A of current (10 A/cm2) were obtained at a voltage of 22.5 kV. The emission of the electron current was carried out with a DC voltage held between the cathode and ground anode. Emission was gated by a l-2 kV, pulse applied across the sample by a solid state or krytron switch. The beam emittance was measured with a mask, phosphor screen and CCD camera; it was found to be 5rt mm mrad yielding a normalized rms heam brightness of 1 .2x101 1 A/m2rad2. This is the first reported measurement of the brightness of a ferroelectric cathode beam; it exceeds that of a thermionic cathode and is close to that of a photocathode. The results for the ferroelectric cathode may be directly compared with a preliminary experiment carried out in the same geometry with a thermionic cathode. The ferroelectric cathode yielded higher current density. obtained electron densities of 10A/cm2 and Ivers et al. [3] of Cornell obtained 70A/cm2. Both groups have measured electron beam current, current density, repetition rate capability and temporal evolution of the emission. In our work we have for the first time measured the quality of the beam produced by a ferroelectric cathode-emittance and brightness. We have obtained a beam current density similar to that of CERN and have shown that the beam is produced with low emittance.

No abstract

The Triassic–Jurassic (Tr–J) boundary marks a major extinction event, which (∼200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr–J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key‐species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites‐Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites–Pinuspollenites Assemblage, and the Sinemurian Perinopollenites–Cycadopites Assemblage. The Tr–J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio–Ferganoconcha and Waagenoperna–Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio–Ferganoconcha and Waagenoperna–Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine‐littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian.

No abstract

No abstract