Abstract: A wireless communication method and apparatus in a wireless local area network (WLAN) system are disclosed. A wireless communication method according to one embodiment may include generating a high-efficiency Wi-Fi (HEW) frame including at least one of an HEW-SIG-A field and an HEW-SIG-B field which include channel information for communications according to an Orthogonal Frequency-Division Multiple Access (OFDMA) mode, and transmitting the generated HEW frame to a reception apparatus.

Abstract: A spiral phase plate, according to one embodiment, for generating a Laguerre Gaussian beam by reflecting an incident beam emitted from a light source, may comprise: a first quadrant area in which the step height increase rate per unit angle decreases progressively in one direction from the point with the lowest step height to the point with the highest step height; and a second quadrant area in which the step height increase rate per unit angle increases progressively in the one direction.

Abstract: Provided are a chromium catalyst precursor, an ethylene oligomerization catalyst including the same, and a method of preparing an ethylene oligomer using the same. More particularly, a chromium catalyst precursor which may oligomerize ethylene with high activity and high selectivity in spite of not using methylaluminoxane (MAO) or modified-methylaluminoxane (MMAO), an oligomerization catalyst including the same, and a method of preparing an ethylene oligomer using the same are provided.

Abstract: The present invention relates to derivatives of polyalkenyl amine substituted with numerous hydroxy groups of the following formula (I) useful as a novel fuel detergent. ##STR1## wherein polyalkenyl denotes a branched alkyl derived from polyolefin which has a molecular weight of 400.about.5,000 and is prepared with olefin having 2 to 6 carbon atoms; m is an integer ranging from 2 to 10, R.sup.1, R.sup.2 and R.sup.3 may be identical or different, and represent a hydrogen atom or a linear or branched alkyl having 1 to 4 carbon atoms: R.sup.4 and R.sup.5 may be identical or different, and denote a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group, a hydroxyalkyl, a phenyl, naphthyl, an aminoalkyl of formula (II) or a polyaminoalkylene of formula (III) ##STR2## wherein R.sup.6 denotes a C.sub.2 -C.sub.10 alkylene group: R.sup.7 and R.sup.8 may be identical or different, and denote a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group, a phenyl, a naphthyl or a C.sub.1 -C.sub.