Methodical basis for comparative analysis of rolling stock modernization economic effectiveness

The article is dedicated to the analytical and methodological issues related to the economic effectiveness appraisal of rolling stock modernization. It is a very current topic because rail carriers often take up decision on comprehensive modernization of the rolling stock, especially locomotives, passenger carriages and multiple units. There was pointed out in the article the necessity of conduction of rolling stock modernization feasibility studies considering three different assumptions: a) assuming the same annual transport efficiency and expecting benefits at the exploitation costs side, b) assuming the same exploitation costs of the new and modernized carriage and expecting benefits at the transport efficiency side, c) assuming varied exploitation costs and varied transport efficiency of the new and modernized rolling stock. Feasibility study should be conducted by the means of discounted cash flow method - increase version, because that method allows best to capture the benefits resulting from the rolling stock modernization.

Fluxes and retention of nutrients and organic carbon in Manko estuary, Okinawa, Japan: influence of river discharge variations

Estuaries are often considered important filters for inorganic and organic nutrients, as they are located between the land and sea. This study reports on the fluvial fluxes and estuarine transformations and retention of dissolved nutrients (total oxidized nitrogen [TON = NO₂⁻ and NO₃⁻]), NH₄⁺, PO₄³⁻, and dissolved organic carbon (DOC) in Manko estuary, Okinawa, Japan. The transport and transformation of dissolved nutrients and DOC varied widely among the eight conducted surveys due to variations in freshwater discharge and subsequent flushing times. Under high fluvial discharge, particularly during the May–June rainy season, the transport of nutrients and DOC accounted for up to 70%, 88%, 93%, and 53% of the annual transport of TON, NH₄⁺, PO₄³⁻, and DOC, respectively. The flushing times of river water into the estuary, which varied from 0.5 to 46 days, were important in determining the degree to which fluvial nutrients were transformed and retained within the estuary. The effect of long flushing times was evident during the dry months (December–March), when biological and geochemical processes within the estuary removed most of the fluvial nutrients and DOC.

Transport of organic carbon from the Mogot Experimental Watershed in the southern mountainous taiga of eastern Siberia

More than 60% of river runoff from the Lena River basin originates in the southern mountainous region of eastern Siberia within the permafrost zone. We studied the transport of dissolved organic carbon (DOC) and particulate organic carbon (POC) within the Mogot Experimental Watershed, which is close to the drainage divide between the Lena and Amur River basins in the southern mountainous taiga region, from 1 August 2000 to 12 November 2001. DOC concentration was strongly related to thawing depth at the bottom of the main valley when thawing depth was less than 20 cm during snowmelt runoff. When thawing depth was equal to or greater than 20 cm, DOC concentration was more closely related to the rate of river discharge in summer runoff. On the basis of our observations, we extrapolated the annual transport of DOC and POC to be 4.75 g C m−2 yr−1 and 0.03 C kg C m−2 yr−1, respectively. Transport of organic carbon from the catchment was about 4.78 g C m−2 yr−1 during 2001. DOC is the main form of organic carbon flux in the study area.