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151.
G. Staccioli R. Seraglia P. Traldi G. Menchi U. Matteoli 《Holz als Roh- und Werkstoff》1994,52(1):39-41
A specimen fromt he fossil forest of Dunarobba (Central Italy) attributed toTaxodioxylon gypsaceum was chemically analyzed particularly for its terpene content. Main chemical constituents show variations related to ageing and carbonization process, while terpene content exhibits a drop of mono- and sesquiterpenes in favour of diterpenes and higher MW compounds. All components are exclusively hydrocarbons and represent alicyclic or partially aromatic structures. The identified families include abietane, phyllocladane, norabietane and norpimarane among diterpenes and traces of cadinane and selinane among sesquiterpenes. 相似文献
152.
Zhi-Gong Wang Berroth M. Nowotny U. Hofmann P. Hulsmann A. Kohler K. Raynor B. Schneider J. 《Solid-State Circuits, IEEE Journal of》1994,29(8):995-997
A monolithically integrated clock recovery (CR) circuit making use of the phase-locked loop (PLL) circuit technique and enhancement/depletion AlGaAs/GaAs quantum well-high electron mobility transistors (QW-HEMT's) with gate lengths of 0.3 μm has been realized. A novel preprocessing circuit was used. In the PLL a fully-balanced varactorless VCO was applied. The VCO has a center oscillating frequency of about 7.7 GHz and a tuning range greater than 500 MHz. A satisfactory clock signal has been obtained at a bit rate of about 7.5 Gb/s. The power consumption is less than 200 mW at a supply voltage of -5 V 相似文献
153.
154.
A. N. Iyer U. Balachandran L. R. Motowidlo J. G. Hoehn P. Haldar 《Journal of Electronic Materials》1994,23(11):1087-1091
Pb0.4Bi1.8Sr2Ca2.2Cu3Ox (Bi-2223) precursor powder was prepared by a solid-state reaction of carbonates and oxides of lead, bismuth, strontium, calcium,
and copper, and the powder was then used to fabricate silver-clad tapes by the powder-in-tube technique. Transport critical
current density (Jc) values>4×104 A/cm2 at 77K and 2×105 A/cm2 at 4.2 and 27K have been achieved in short tape samples. Long lengths of tape were tested by winding them into pancake coils.
Recently, we fabricated a test magnet by stacking ten pancake coils, each containing three 16m lengths of rolled tape, and
tested it at 4.2, 27 and 77K. A maximum generated field of 2.6 T was measured in zero applied field at 4.2K and the test magnet
generated significant self-field in background fields up to 20 T. The results are discussed in this paper. 相似文献
155.
156.
This paper presents a 20-Gb/s 1:4-demultiplexer for future fiber-optic transmission systems. It uses an 0.4-μm emitter double polysilicon 21-GHz fT Si bipolar foundry process. This is the highest data rate of a 1:4-DEMUX reported so far in any technology. The 1:4-DEMUX features a tree-type architecture with one frequency divider and a channel switch circuit. The circuit design was carefully optimized to achieve high speed and moderate power dissipation. It consumes 1.4 W with a single -4.5-V supply 相似文献
157.
High-power passively mode-locked semiconductor lasers 总被引:8,自引:0,他引:8
Haring R. Paschotta R. Aschwanden A. Gini E. Morier-Genoud F. Keller U. 《Quantum Electronics, IEEE Journal of》2002,38(9):1268-1275
We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties 相似文献
158.
U Ziemann M Winter CD Reimers K Reimers F Tergau W Paulus 《Canadian Metallurgical Quarterly》1997,49(5):1292-1298
We investigated 14 patients with amyotrophic lateral sclerosis (ALS) by paired conditioning-test transcranial magnetic stimulation to test the hypothesis that the motor cortex is hyperexcitable in ALS. Intracortical (corticocortical) inhibition was significantly less in the ALS group than in an age-matched healthy control group (85.3 +/- 27.0% versus 45.2 +/- 15.5%, respectively; p < 0.0001). In contrast, intracortical facilitation, motor threshold, and cortical silent period duration in the ALS patients were not different from the control group. We suggest that the selective abnormality of intracortical inhibition is best compatible with an impaired function of inhibitory interneuronal circuits in the motor cortex that in turn renders the corticomotoneuron hyperexcitable. 相似文献
159.
A Egesten I H?gerstrand U Kristoffersson S Garwicz 《Canadian Metallurgical Quarterly》1997,96(2):369-373
Fibroblast growth factors are important heparin binding, mitogenic proteins. The binding site in heparin and heparan sulfate for fibroblast growth factor-2 (basic fibroblast growth factor) has been described as rich in glucosamine-2-sulfate 1-->4 linked to iduronic acid-2-sulfate. The glucosamine residue in the heparin binding site is also 6-sulfated. A new glycosaminoglycan, acharan sulfate, has been chemically modified to prepare a polysaccharide, N-sulfoacharan sulfate, consisting of glucosamine-2-sulfate 1-->4 linked to iduronic acid-2-sulfate. Acharan sulfate binds very weakly to fibroblast growth factor-2 while N-sulfoacharan sulfate binds with nearly the same affinity as heparin. Mitogenicity studies were performed using heparan sulfate-free cells stably transfected with fibroblast growth factor receptor-1. Acharan sulfate inhibits heparin's enhancement of fibroblast growth factor-2 mitogenic activity, without affecting cell viability, while N-sulfoacharan sulfate shows heparin-like activity but at a greatly reduced level. These results suggest additional mechanisms not requiring high affinity glycosaminoglycan binding to fibroblast growth factor-2 may be important in its mitogenic activity. 相似文献
160.