Ⅰ. INTRODUCTION Welsh conjectured that on average a matroid has fewer circuits than the bases it has. But he has not found a way to prove his conjecture. Up to now the reports on this respect are very few. Quirk and ...
Lithium tantalate (LiTaO3) single crystal is one of the most important ferroelectric crystals for its excellent piezoelectric, pyroelectric and photoelectric properties. Many of its physical properties have been wid...