검색결과

검색조건
좁혀보기
검색필터
결과 내 재검색

간행물

    분야

      발행연도

      -

        검색결과 12

        1.
        2024.03 KCI 등재 구독 인증기관·개인회원 무료
        The cocoa sub-sector is an important pillar of Ghana’s economic stability and growth prospects; the sub-sector contributes to fiscal stability, infrastructure, and employment. In recent times, diversification has become a common observable feature in the industry. This study uses the conditional mixed process approach to examine the interaction between the diversification status and profitability of cocoa farming simultaneously in a single system. Using data from 401 farmers in the Western and Ashanti regions of Ghana in 2022, the study found that more profitable farmers were more likely to diversify. Conversely, diversified farmers were likely to be more profitable than non-diversified farmers. It also found that the farmer's age, experience, farm area, and location of the farm impacted both the profitability and diversification status of farmers. Thus, it is suggested that policymakers should direct policies and programs to support the creation of alternative farm-based livelihoods for farmers.
        2.
        2022.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        PURPOSES : A mechanistic-empirical (ME) predictive design logic that can compute the reflective cracking life of hot-mix asphalt (HMA) overlaid on top of a composite pavement is proposed herein. METHODS : The overlay thickness design and analysis logic of the HMA were formulated based on the ME concept of reflection crack propagation. Climate data, traffic load data, the pavement material properties, and the thickness of each layer of the pavement are the main inputs for the ME-Reflective Cracking Rate (RCR) prediction algorithm. An Microsoft Excel Virtual Basic for Application (VBA) program was created to aid designers in assessing the expected performance of an HMA overlay design. Calibration was done using data from the Long-Term Pavement Performance (LTPP) sections. Sensitivity analysis was conducted to compare the results yielded by the program and data from a report by the Texas Transportation Institute. RESULTS : The predictive model performance effectively generates the dynamic and relaxation modulus curves. The correlation value of the calibration factors, R2, is 0.79. The calibration factors used for the Asphalt Overlay Thickness Design (AOTD) program and the sensitivity analysis, i.e., k1, k2,, and k3,, are set to 5, 5, and 150, respectively. The sensitivity of the AOTD program affords reasonable results. Additionally, the program yields results similar to the trends presented in a report by the Federal Highway Administration. CONCLUSIONS : The proposed ME design logic is successfully translated into an Excel VBA program, AOTD, which can perform routine assessments of laboratory tests for HMA overlays. The program can effectively perform numerous iterations and computations to predict an HMA overlay. The predictive model can generate reasonable dynamic modulus and relaxation modulus curves for the characterization of HMA overlays. Under the same asphalt binder grade and HMA type, doubling the HMA overlay thickness yields three times the expected reflective cracking service life.
        4,000원
        4.
        2017.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        This paper reviews the requirements for far-infrared astronomy in the period following the SPICA satellite in the late 2020's. We take a very long view of the state of FIR astronomy and what facilities will be required in a twenty year timeframe. We show that spatial resolution to match that of observatories operating in the optical and mid-infrared and the radio will be a necessity. Moreover this high spatial resolution must be combined with high spectral and photometric sensitivity to provide the data required to further our understanding of planetary formation mechanisms, the history of star formation through cosmic time and the feedback between active galactic nuclei and their host galaxies in controlling star formation. We review three possible conceptual mission scenarios and comment on the possibility of realising them in the coming deades.
        4,000원
        5.
        2016.12 구독 인증기관 무료, 개인회원 유료
        On Cheju Island something happened in ‘peacetime’ under the American Occupation-namely a major peasant war-and after decades of repression Cheju people finally have came forward to tell their stories and demand compensation, and no special pleading about the exigencies of wartime will suffice to assuage the American conscience. What formerly classified American materials document is a merciless, wholesale assault on the people of this island. No one will ever know how many died in this onslaught, but the American data, long kept secret, ranged between 30,000 and 60,000 killed, with upwards of 40,000 more people having fled to Japan (where many still live in Osaka). There were at most 300,000 people living on Cheju Island in the late 1940s.1 This happened when the U.S. was legally responsible for actions taken under its command, but as it happened, instead of punishing the criminals, American leaders directed the suppression of the rebellion and were pleased when it was crushed. The effective political leadership on Cheju until early 1948 was provided by strong leftwing people’s committees that first emerged in August 1945, and later continued under the American Occupation (1945-1948). The Occupation preferred to ignore Cheju rather than to do much about the committees; it appointed a formal mainland leadership but let the people of the island run their own affairs. The result was an entrenched leftwing, one with no important ties to the North and few to the South Korean Workers Party (SKWP) on the mainland; the island was also well and peaceably governed in 1945-47, particularly by contrast to the mainland. In early 1948 as Syngman Rhee and his American supporters moved to institute his power in a separate southern regime, however, the Cheju people responded with a strong guerrilla insurgency that soon tore the island apart.
        4,000원
        6.
        2006.04 구독 인증기관·개인회원 무료
        Dimensional precision is a critical parameter in net shape processing of ferrous PM components. Sinter-hardening alloys undergo a transformation from austenite to martensite. Martensite formation expands the sintered compact, while tempering hardened steels results in shrinkage. In addition, martensitic regions with high Cu and C contents may contain large amounts of retained austenite. The presence of martensite and retained austenite, in addition to the tempering step, all play a role in the final dimensions of a component. This paper investigates the dimensional and microstructural changes to two sinter-hardening grades through different post-sintering thermal treatments.
        7.
        2006.04 구독 인증기관·개인회원 무료
        Machining of sinter-hardened PM steels provides a challenge for part makers. To facilitate machining of these materials, a new additive (MA) has been developed to increase tool life during the machining process. Hard turning tests were performed to evaluate the effect of this new additive. Sintered compacts with the MA additive were compared to compacts without a machining aid and to compacts that contained the MnS additive. This paper discusses the improvement in machinability with this new additive in sinter-hardenable PM steels.
        8.
        2006.04 구독 인증기관·개인회원 무료
        Ancorsteel 4300, a high performance Cr-Si-Ni-Mo steel, was unveiled two years ago as the first in a series of powder metallurgy alloys that will simulate wrought steel compositions. Advantages of this alloy include good compressibility, high hardenability, and excellent dimensional stability. More important, however, is that this alloy has the ability to be effectively sintered at and maintain oxygen contents below 500 ppm. This unique blend of performance and processing capabilities provides static and dynamic properties that exceed those of conventional powder metallurgy alloys and approach wrought gearing materials. A second Cr-Si-Ni-Mo alloy has now been developed that offers complimentary performance levels at a lower Mo content. This manuscript reviews properties of the two chromium steels with comparisons to traditional sinter-hardened and heat-treated powder metallurgy alloys.
        10.
        2012.03 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        After a visit by Peter Waddell from the University of Strathclyde, Glasgow, UK in 1991, Robert H. Koch launched a program at the University of Pennsylvania to build lightweight pneumatic membrane mirrors, initially for balloon flight observa\-tions where weight is at a premium. Mirror cells were fabricated from sizes 0.18 m to 1.77 m, and experiments conducted to characterize the mirror figure and stability. Most of the work stopped after Prof. Koch’s retirement in 1996 until 2006 when the authors expressed an interest in building an array of medium-aperture portable telescopes. The program re\-started in earnest at Gravic, Inc. in Malvern, PA in 2008 with Koch using his extensive observational astronomy experience to guide the fabrication of a fully operational 1.07 m membrane mirror telescope with an optical tube assembly weigh\-ing under 45 Kg. Residual wavefront aberrations remediation resulted in Koch and the authors investigating membrane tensioning techniques with different cell designs, active secondary wavefront correction, photometric algorithms for ab\-errated images, and the use of additional lightweight mirror substrates from the Alt-Az Initiative Group, such as foamed glass. The best result for the lightweight mirrors was a point spread function spot size of several arc seconds. A lightweight 1.6 m cast aluminum cell alt-az telescope was subsequently designed by Koch and the authors for prime focus use.
        11.
        2012.03 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        This report describes the inception, development and extensive use over 30 years of elliptical polarimeters at the Uni\-versity of Pennsylvania. The initial Mark I polarimeter design utilized oriented retarder plates and a calcite Foster-Clarke prism as the analyzer. The Mark I polarimeter was used on the Kitt Peak 0.9 m in 1969-70 to accomplish a survey of ap\-proximately 70 objects before the device was relocated to the 0.72 m reflector at the Flower and Cook Observatory. Suc\-cessive generations of automation and improvements included the early-80’s optical redesign to utilize a photoelastic modulated wave plate and an Ithaco lock-in amplifier–the photoelastic modulating polarimeter. The final design in 2000 concluded with a fully remote operable device. The legacy of the polarimetric programs includes studies of close binaries, pulsating hot stars, and luminous late-type variables.
        12.
        2012.03 KCI 등재 SCOPUS 서비스 종료(열람 제한)
        Binary companions are often invoked to explain the axial and point symmetry seen in the majority of planetary nebulae and proto-planetary nebulae (PPNs). To explore this hypothesis, we have undertaken a long-term (20 year) study of light and velocity variations in PPNs. From the photometric study of 24 PPNs, we find that all vary in brightness, and from a subset of 12 carbon-rich PPNs of F-G spectral type we find periods of 35-155 days, with the cooler having the longer pe\-riods. The variations are seen to be due to pulsation; no photometric evidence for binarity is seen. A radial velocity study of a sub-sample of seven of the brightest of these shows that they all vary with the pulsation periods. Only one shows evidence of a longer-term variation that we tentatively identify as being due to a binary companion. We conclude that the present evidence for the binary nature of these PPNs is meager and that any undetected companions of these PPNs must be of low mass (< 0.25 M ) or long period (> 30 years).