title: Modeling seasonality in new product diffusion

authors: Peers, Y.

subjects: diffusion models

abstract: We propose a method to include seasonality in any diffusion model that has a closed-form solution. The resulting diffusion model captures seasonality in a way that naturally matches the original diffusion model’s pattern. The method assumes that additional sales at seasonal peaks are drawn from previous or future periods. This implies that the seasonal pattern does not inﬂuence the underlying diffusion pattern. The model is compared with alternative approaches through simulations and empirical examples. As alternatives, we consider the standard Generalized Bass Model (GBM) and the basic Bass Model, which ignores seasonality. One of the main ﬁndings is that modeling seasonality in a GBM generates good predictions but gives biased estimates. In particular, the market potential parameter is underestimated. Ignoring seasonality in cases where data of the entire diffusion period are available gives unbiased parameter estimates in most relevant scenarios. However,ignoring seasonality leads to biased parameter estimates and predictions when only part of the diffusion period is available. We demonstrate that our model gives correct estimates and predictions even if the full diffusion process is not yet available.

text: Modeling seasonality in new product diffusion We propose a method to include seasonality in any diffusion model that has a closed-form solution. The resulting diffusion model captures seasonality in a way that naturally matches the original diffusion model’s pattern. The method assumes that additional sales at seasonal peaks are drawn from previous or future periods. This implies that the seasonal pattern does not inﬂuence the underlying diffusion pattern. The model is compared with alternative approaches through simulations and empirical examples. As alternatives, we consider the standard Generalized Bass Model (GBM) and the basic Bass Model, which ignores seasonality. One of the main ﬁndings is that modeling seasonality in a GBM generates good predictions but gives biased estimates. In particular, the market potential parameter is underestimated. Ignoring seasonality in cases where data of the entire diffusion period are available gives unbiased parameter estimates in most relevant scenarios. However,ignoring seasonality leads to biased parameter estimates and predictions when only part of the diffusion period is available. We demonstrate that our model gives correct estimates and predictions even if the full diffusion process is not yet available.

year: 2012

title: Marine tephrochronology: A personal perspective

authors: Lowe, David J.

abstract: This special volume on marine tephrochronology is remarkable, and timely, because it marks a concerted step towards what might be informally termed ‘phase 3’ of a revolution in Quaternary geosciences that began around 40 years ago. The 10 articles collectively represent a re-focussed examination of tephras and cryptotephras preserved in ocean sediments at various locations and the authors describe their significance for a range of subdisciplines. Eight articles provide a new understanding of the origin, distribution and ages of various tephra and cryptotephra deposits and their stratigraphic inter-relationships; how the terrestrial ages of the tephra/crypotephra deposits relate to those of enclosing sediments and inform the ongoing development of the marine radiocarbon time-scale; mechanisms for the emplacement, remobilization or bioturbation of the tephras or cryptotephras; and volcanic eruption history. Two further articles document the characterization of tephra-derived glass shards using microbeam techniques to analyse 30–40 elements from individual shards as small as 10 µm in diameter. The collection thus provides snapshots of many aspects of the latest developments and directions in tephra studies – volcanology, primary and secondary dispersal, stratigraphy, single-grain characterization, chronology – through the medium of marine sediments. My personal perspective reflects briefly on how this point was reached and identifies a few of the important milestones on the way from ‘phase 1’ to ‘phase 3’. I am privileged to write it. Marine science revolution As an undergraduate in the early-mid 1970s, I recall my first real ‘awakening’ regarding the dynamic nature of science, and of Quaternary geoscience in particular, when told about deep-sea core V28-238 from the equatorial Pacific Ocean (Shackleton & Opdyke 1973; >2650 citations, Google Scholar). Analogous to the opening notes of Beethoven's 5th Symphony, perhaps the most famous quartet of notes in history, the alpha-numerical assemblage ‘V28-2

text: Marine tephrochronology: A personal perspective This special volume on marine tephrochronology is remarkable, and timely, because it marks a concerted step towards what might be informally termed ‘phase 3’ of a revolution in Quaternary geosciences that began around 40 years ago. The 10 articles collectively represent a re-focussed examination of tephras and cryptotephras preserved in ocean sediments at various locations and the authors describe their significance for a range of subdisciplines. Eight articles provide a new understanding of the origin, distribution and ages of various tephra and cryptotephra deposits and their stratigraphic inter-relationships; how the terrestrial ages of the tephra/crypotephra deposits relate to those of enclosing sediments and inform the ongoing development of the marine radiocarbon time-scale; mechanisms for the emplacement, remobilization or bioturbation of the tephras or cryptotephras; and volcanic eruption history. Two further articles document the characterization of tephra-derived glass shards using microbeam techniques to analyse 30–40 elements from individual shards as small as 10 µm in diameter. The collection thus provides snapshots of many aspects of the latest developments and directions in tephra studies – volcanology, primary and secondary dispersal, stratigraphy, single-grain characterization, chronology – through the medium of marine sediments. My personal perspective reflects briefly on how this point was reached and identifies a few of the important milestones on the way from ‘phase 1’ to ‘phase 3’. I am privileged to write it. Marine science revolution As an undergraduate in the early-mid 1970s, I recall my first real ‘awakening’ regarding the dynamic nature of science, and of Quaternary geoscience in particular, when told about deep-sea core V28-238 from the equatorial Pacific Ocean (Shackleton & Opdyke 1973; >2650 citations, Google Scholar). Analogous to the opening notes of Beethoven's 5th Symphony, perhaps the most famous quartet of notes in history, the alpha-numerical assemblage ‘V28-2

year: 2014

title: Studies on the conservation of waterlogged wood in New Zealand

authors: Wallace, Roderick Thomas

abstract: This thesis is a study of properties of certain New Zealand woods recovered from waterlogged environments. The woods are those which were commonly used by the pre-european Maori to make artefacts, and the properties are those which affect the way these artefacts can be conserved after they have been removed from wet archaeological sites.
The properties studied were (a) the species of wood used (b) the forms and shapes of the timbers (c) the densities (d) directional shrinkages, and (e) directional penetrabilities of each wood. The results of this research are intended to aid conservators to correctly treat the artefacts. 
The research began with studies of (a) New Zealand wet site archaeology, (b) the structure and properties of wood in general, and (c) the techniques used to conserve waterlogged wood worldwide.
This was followed by a survey of circa. 1000 wooden Maori artefacts from Museums involving the identification, by thin section microscopy, of wood species. 30 wood types from 22 tree species were found to have been widely used. A collection was made of samples of each type in different states of decay. 
Each sample was tested for density, directional shrinkage and directional penetrability.
The penetrability was measured by vacuum impregnation of water into wood blocks. Results were compared to those from sound oak (Quercus robur), a wood which has been studied intensively by conservators in Europe. 
Detailed summaries of the conservation properties of 26 wood types are given. This reveals that while some New Zealand woods are easy to conserve others provide considerable problems. The latter woods are all highly durable in wet sites, extremely dense, have high shrinkages and are highly impenetrable. These will require special types of treatment to avoid damage during conservation.

text: Studies on the conservation of waterlogged wood in New Zealand This thesis is a study of properties of certain New Zealand woods recovered from waterlogged environments. The woods are those which were commonly used by the pre-european Maori to make artefacts, and the properties are those which affect the way these artefacts can be conserved after they have been removed from wet archaeological sites.
The properties studied were (a) the species of wood used (b) the forms and shapes of the timbers (c) the densities (d) directional shrinkages, and (e) directional penetrabilities of each wood. The results of this research are intended to aid conservators to correctly treat the artefacts. 
The research began with studies of (a) New Zealand wet site archaeology, (b) the structure and properties of wood in general, and (c) the techniques used to conserve waterlogged wood worldwide.
This was followed by a survey of circa. 1000 wooden Maori artefacts from Museums involving the identification, by thin section microscopy, of wood species. 30 wood types from 22 tree species were found to have been widely used. A collection was made of samples of each type in different states of decay. 
Each sample was tested for density, directional shrinkage and directional penetrability.
The penetrability was measured by vacuum impregnation of water into wood blocks. Results were compared to those from sound oak (Quercus robur), a wood which has been studied intensively by conservators in Europe. 
Detailed summaries of the conservation properties of 26 wood types are given. This reveals that while some New Zealand woods are easy to conserve others provide considerable problems. The latter woods are all highly durable in wet sites, extremely dense, have high shrinkages and are highly impenetrable. These will require special types of treatment to avoid damage during conservation.

year: 1985