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We give an algebraic proof of a class number formula for dihedral extensions of number fields of degree 2q, where q is any odd integer. Our formula expresses the ratio of class numbers as a ratio of orders of cohomology groups of ...
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We give an algebraic proof of a class number formula for dihedral extensions of number fields of degree 2q, where q is any odd integer. Our formula expresses the ratio of class numbers as a ratio of orders of cohomology groups of units and allows one to recover similar formulas which have appeared in the literature. As a corollary of our main result, we obtain explicit bounds on the (finitely many) possible values which can occur as ratio of class numbers in dihedral extensions. Such bounds are obtained by arithmetic means, without resorting to deep integral representation theory.
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Due to the entry into force in 2014 of the European F-Gas Regulation n 517/2014 and the subsequent Kigali amendment, the phase-out of the medium and high-GWP refrigerants has speeded up in all refrigeration fields. The effect on t...
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Due to the entry into force in 2014 of the European F-Gas Regulation n 517/2014 and the subsequent Kigali amendment, the phase-out of the medium and high-GWP refrigerants has speeded up in all refrigeration fields. The effect on the plug-in or stand-alone systems has meant that other environmentally friendly refrigerants must replace the R134a with low or ultra-low GWP maintaining the same operating conditions and reducing the energy consumption. Extended examples of these fluids are the hydrocarbons R600a and R290 and the inorganic fluid R744 (CO2). However, there are other alternatives to the HFCs R152a and R1234yf or the hydrocarbon R1270 that have hardly been analysed and can make a positive contribution to this sector. Accordingly, this work aims to evaluate the behaviour of a commercial beverage cooler experimentally when it is optimised with six alternatives to the HFC R134a: R152a, R1234yf, R290, R1270, R600a and R744. Results demonstrated that fluids R290, R1270, R152a, R744 and R600a reduce the energy of R134a in 27.5%, 26.3%, 13.7%, 3.9% and 1.2%, respectively, while the use of R1234yf increases the energy usage to 4.1%.
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This paper uses annual data from 31 provinces, municipalities and autonomous regions in China from 2000 to 2018 to examine the determinants of Chinese house prices with a panel data regression method. Our finding suggests that lan...
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This paper uses annual data from 31 provinces, municipalities and autonomous regions in China from 2000 to 2018 to examine the determinants of Chinese house prices with a panel data regression method. Our finding suggests that land price, loans of real estate developers, per capita saving and the proportion of people with college or above educational degrees significantly drive up house prices, while the number of unemployed population has a significant negative impact. These five variables account for 72 percent variations in house prices across the country. Other economic fundamentals such as inflation, interest rate, per capita gross domestic products (GDP), and rent cost do not have significant influences on house prices. The econometric model is then used to assess the existence of house price bubbles in those provincial-level divisions in China by comparing their actual price levels with those predicted by the model. If the trend of house price growth during 2002-2014 found in the present study is the true long-run trend of house prices in China, with a few exceptions, the house prices in most provincial-level divisions are not overvalued by the end of 2014.
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In this article, we study some variants of the Bombieri-Vinogradov theorem for number fields. We refine the level of distribution in the previous work of Murty-Petersen. When investigating the short interval version, we give a new...
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In this article, we study some variants of the Bombieri-Vinogradov theorem for number fields. We refine the level of distribution in the previous work of Murty-Petersen. When investigating the short interval version, we give a new zero density estimate of large sieve type, unlike the result of Hinz which is directly used in Thorner's work. Further, we strengthen the result of Thorner for the Bombieri-Vinogradov theorem in short intervals. As applications, we improve some numerical results on the bounded gaps of primes in Chebotarev sets and the Euclidean algorithm for S-integers.
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Recent studies that estimated the land use-travel relationship while controlling for residential self-selection mostly acknowledged the potential for the self-selection in the reverse direction according to learning and self-justi...
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Recent studies that estimated the land use-travel relationship while controlling for residential self-selection mostly acknowledged the potential for the self-selection in the reverse direction according to learning and self-justification over time. Thus, this study empirically tests how the relationship varies by the length of time after residential move in Seoul, South Korea. Analytical results show that population density encourages the choice of automobile alternatives in extreme cases, that is, for newly moved first-year residents who decided to tolerate congestion and for longtime residents of 4 years or more who had a due chance to learn and appreciate neighborhood travel options and also, it extends commuting time for these short and longtime residents. Employment density reduces commuting time for all but longtime residents because of better jobs-housing balance while it is not necessarily accompanied by mode choice variations. Street intersection density is associated with commuting time variations in all cases. Land use balance entropy is unrelated to the time variations, but consistently related to the alternative mode choice, and possibly beneficial to trip-chaining. While public transit densities are classified into subway and bus densities, the former turns out to be significant regarding commuting time and mode choice for most residents, but the latter only for first-year residents. Particularly on the mode choice, the gradual learning effect is associated with subway density (significant after 1 year), whereas the self-justification effect by bus density is rather quick, but not lasting (significant only for 1 year).
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This work analyses the influence of the Internal Heat Exchan ger (IHX) on the energy performance of a vapor compression cycle associated with a freezing cabinet using different R404A low-GWP alternatives. Among them, the refrigera...
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This work analyses the influence of the Internal Heat Exchan ger (IHX) on the energy performance of a vapor compression cycle associated with a freezing cabinet using different R404A low-GWP alternatives. Among them, the refrigerants R454C (GPW100=146), R455A (GPW100=146), R468A (GPW100=146), R290 (GPW100=5) and R1270 (GPW100=1.8) have been tested in a horizontal freezing cabinet maintaining a product target temperature of -20°C at the heat rejection temperatures of 20, 30 and 40°C. The results from tests show that the use of the IHX reduces energy consumption in all scenarios without significantly increasing the compressor's discharge temperature. For a test period of 16 h, the refrigerants that offer better reductions are R404A and R1270, followed by R455A, R290, R454C and R468A. The maximum energy saving is rated to 9.2% at the heat rejection temperature of 40°C, demonstrating that the enhancement of the IHX is better as higher the heat rejection conditions are.
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This paper shows that a positive proportion of the imaginary quadratic fields with 2-class rank equal to 3 have 4-class rank equal to zero and infinite Hilbert 2-class field towers.
摘要 :
Let
p
≡
3
...
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Let
p
≡
3
(
mod
4
)
{p\equiv 3\pmod{4}}
and
l
≡
5
(
mod
8
)
{l\equiv 5\pmod{8}}
be different primes such that
p
l
=
1
{\frac{p}{l}=1}
and
2
p
=
p
l
4
{\frac{2}{p}=\frac{p}{l}_{4}}
. Put
k
=
?
?
(
l
)
{k=\mathbb{Q}(\sqrt{l})}
, and denote by ? its fundamental unit. Set
K
=
k
?
(
-
2
?
p
?
?
?
l
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摘要 :
Приведены результаты изучения ритма сезонного развития (2002—2013 гг.) 10 видов рода Rosa L., интродуцированных в парк Ботанического с...
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Приведены результаты изучения ритма сезонного развития (2002—2013 гг.) 10 видов рода Rosa L., интродуцированных в парк Ботанического сада Ботанического института. Степень зимостойкости видов зависит от степени синхронности окончания вегетации с окончанием вегетации местными древесными породами. В озеленении Санкт-Петербурга можно широко использовать зимостойкие виды R. altaica, R. amblyotis, R. davurica, R. myriacantha, R. glauca, R. rugosa, R. spinosissima и сравнительно зимостойкие R. gallica и R. sweginzowii.
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