The structural phase transformations of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) were studied using high resolution x-ray diffraction (HRXRD) as a function of temperature and electric field. A phase transformational sequence of cubic (C)→tetragonal (T)→rhombohedral (R) phase was observed in zero-field-cooled conditions; and a C→T→monoclinic (Mc)→ monoclinic (MA) phase was observed in the field-cooled conditions. The transformation of T to MA phase was realized through an intermediate Mc phase. The results also represent conclusive and direct evidence of a Mc to MA phase transformation in field-cooled conditions. Beginning from the zero-field-cooled condition, a R→MA→Mc→T phase transformational sequence was found with an increasing electric field at a fixed temperature. Upon removal of the field, the MA phase was stable at room temperature. With increasing the field, the transformation temperature from T to Mc and from Mc to MA phase decreased, and the phase stability ranges of both T and Mc phases increased. Upon removal of the field, the phase transformation from R to MA phase was irreversible, but from MA to Mc was reversible, which means that MA is the dominant phase under the electric field. In the M phase region, the results confirmed that lattice parameters and tilt angles were weakly temperature dependent over the range of investigated temperatures.

The dielectric properties and phase transformation of poled <001>-oriented Pb(Mg1/3Nb2/3)O3-x%PbTiO3(PMN-x%PT) single crystals with compositions of x=20, 30, and 35mole% are investigated for orientations both parallel andperpendicular to the [001] poling direction. An electric-field-induced monoclinic phase was observed for the initial poled PMN-30PT and PMN-35PT samples by means of high-resolution synchrotron x-ray diffraction. The monoclinic phase appears from−25oC to 100oC and from −25oC to 80oC for the PMN-30PT and PMN-35PT samples, respectively. The dielectric constant (ε)-temperature (T) characteristics above the Curie temperature were found to be described by the equation(1/ε−1/εm)1/n=(T−Tm)/C, where εm is the maximum dielectric constant and Tm is the temperature giving εm, and n and C are constants that changewith the composition. The value of n was found to be 1.82 and 1.38 for 20PT and 35PT, respectively. The results of meshscans and the temperature-dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a singledomain tetragonal phase and a to paraelectric cubic phase. In the ferroelectric tetragonal phase with a single domain state, thedielectric constant measured perpendicular to the poling direction was dramatically higher than that measured in the paralleldirection. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believedto be related to dielectric softening close to the morphotropic phase boundary.

The structure and dielectric properties of poled<001>-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) crystals have been investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric field induced monoclinic phase was observed for the initial poled sample. The phase remained stable after the field was removed. A quite different temperature dependence of dielectric constant has been observed between heating and cooling due to an irreversible phase transformation. The results of mesh scans and temperature dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase at 370K and to a paraelectric cubic phase at 405K upon heating. However, upon subsequent cooling from the unpoled state, the cubic phase changes to a poly domain tetragonal phase and to a rhombohedral phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that of the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary and at the phase transition temperature.

A method for evaluating bulk sensitive structural characteristics of unpurified, as-purified, and acid treated single walled carbon nanotubes (SWNTs) was described in the present study. The optical spectra of SWNT solutions were well resolved after prolonged sonication and they were correlated to the diameter and the distribution of nanotubes. The acid-treated SWNTs were similar to as-purified SWNTs in terms of catalyst residue, radial breathing mode (RBM) in the Raman spectra, and the first band gap energy of semiconducting tubes in the optical spectra. The solution phase optical spectra were more sensitive to changes in the small diameter and metallic tubes after the acid treatment than were the RBM spectra.

The objectives of this paper are to present data to illustrate how an advanced digestion process, two-phase digestion, can provide superior performance in terms of waste stabilization efficiency and net energy recovery. As the result, it is possible to separate enrichment cultures of acidogenic and methanogenic organisms in isolated environments by kinetic control involving manipulation of dilution rates. In single-phase digestion process, HRT and COD loading for effective operation were 14.29 days and 2.33kg $COD/m^3$ day, but two-phase digestion may be conducted efficiently at 7 days of HRT and 5.71kg $COD/m^3$ day of loading. Data from this studies showed that the two-phase process is better than single-phase digestion under all test conditions when compared on the bases of gas yield and production rate, reductions of COD and VS, buffer capacity, and unconverted volatile acids in the effluent.

혐기성소화 공정은 기본적으로 가수분해단계(Hydrolysis), 산생성 단계(Acidogenesis), 메탄생성단계(Methanogenesis) 총 3단계로 구분지울 수 있으며, 메탄생성단계에서 아세트산(Acetic acid)과 수소 등의 유기물이 메탄으로 전환되면서 혐기발효의 안정화가 이루어진다. 유기성 폐기물의 혐기성 소화는 유기성 폐기물을 기질로 하여 가수분해와 산발효 및 메탄발효 과정을 통하여 메탄으로 생성된다. 혐기 발효 시 유기산과 pH 변화는 혐기발효의 중요한 영향인자 중 하나이며, 혐기 발효의 안정성을 판단할 수 있는 지표가 된다. 본 연구에서는 보편적으로 사용되는 단상 혐기 발효조를 이용하여 투입되는 유기물(VS)농도, 원료배합(돈분 중 분 성분이 30%, 뇨 성분이 70%) 등 운전조건의 변화에 따라 유기성 폐기물의 혐기성 발효가 진행되는 과정을 분석하였으며, 발효 과정 중 생성되는 아세트산, 프로피온산, 부틸산 등 총 9종류의 유기산 분석과 이에 따른 바이오가스 생산량과 메탄발생량을 분석하였다. 혐기성 발효조는 호기성 산화열을 이용하여 혐기성 소화조를 간접적으로 가온하였으며, 중온 혐기성 소화를 진행하였다. 음식물류 폐기물과 돈분뇨 혼합비에 따라 CASE 1, CASE 2, CASE 3로 분류하였으며, CASE 1의 비율은 음식물류 폐기물 8kg과 돈분뇨 20L, CASE 2 음식물류 폐기물 10kg과 돈분뇨 20L, CASE 3는 음식물류 폐기물 8kg과 물 20L의 조건으로 실험을 진행하였다. 본 실험에서 혐기성 소화조의 pH는 평균 8.17로 나타내어 안정적인 혐기 소화 효율을 나타내었다. 혐기성 소화조의 온도는 평균적으로 38℃로 중온소화가 가능한 것으로 확인되었다. 혐기성 발효 과정 중 생성된 유기산의 농도는 33.67∼1,452.81mg/L로 분석되었다. 일반적으로 혐기발효시 안정적인 VFA의 농도는 500mg/L 이하이며, 운전기간 동안 전체 유기산 농도는 432.86mg/L로 분석되어 안정적인 혐기 발효가 진행되었다고 판단하였다. 바이오가스 발생량의 경우 CASE 1에서 0.29~0.31㎥/day로 나타났으며, CASE 2는 0.325㎥/day로 나타났다. 본 연구를 통하여 혐기 발효시 발생되는 유기산 농도와 pH 변화에 따라 유기성 폐기물의 혐기 발효 시 안정성을 판단한 결과 운전기간 동안 혐기발효는 안정적으로 이루어 졌다고 판단되었다.

단일절리에서 2상유체의 거동을 모의하기 위해 개발된 수치모형의 검증을 위해서 상대투과계수 특성식을 수치모형에 적용하여 가스와 물의 동시거동을 해석한 후, 수치모의 결과를 모형실험결과와 비교하였다. 절리면의 거칠기와 간극의 크기에 댸한 민감도 분석을 실시한 결과, 가스의 이동속도는 절리면의 거칠기와 반비례하였으며, 절리간극의 크기와는 상대투과계수 특성식의 영향으로 단상유체의 흐름에서와 같은 간극크기의 제곱에 비례하는 향상은 보이지 않았다. 수치모형의 현장

본 연구에서는 단일절리에서 2상유체 동시거동을 해석하기 위해서 2차원 유한차분 수치모형을 개발하였다. 개발된 모형은 압력에 따른 점성의 변화가 포화도에 따른 상대투과계수의 변화를 절리간극의 크기별로 고려할 수 있다. 수치기법으로는 IMPES해법을 적용하여 물과 가스의 압력변화량과 포화도를 차례로 구하였다. 개발된 수치 모형에 이용할 상대투과계수의 특성식 도출을 위해서 일곱가지 경우의 평판모형실험을 실시하였다. 실험으로부터 도출된 상대투과계수 특성곡선은