Chronologies and timelines

 

Chronologies are simple but useful tools that help order events sequentially; display information graphically; and identify possible gaps, anomalies, and correlations. The technique pulls the analyst out of the evidentiary weeds to view a data set from a more strategic vantage point. A Chronology places events or actions in the order in which they occurred. A Timeline is a visual depictions of those events showing both the time of events and the time between events. Chronologies can be paired with a Timeline and mapping software to create geospatial products that display multiple layers of information such as time, location, and multiple parallel events. The geographic scope and many details of this case make a Chronology, Timeline, and Map particularly useful in understanding how the case unfolded both temporally and spatially.

Deliverable 1:

Create a Chronology of the anthrax attacks and investigation

Step 1: Identify the relevant information from the case narrative with the date and order in which it occurred.

Step 2: Review the Chronology by asking the following questions:

What does the timing of the appearance of symptoms tell me about when the letters were mailed?
Could there be any other letters than the four in the government’s possession?
What additional information should we seek?
Are there any anomalies in the timing of events?
Deliverable 2:

Create a Timeline of the attacks based on geographic location.

Step 1: Identify the relevant information about the victims from the Chronology with the date and order in which the events occurred. Consider how best to arrange the data along the Timeline. Can any of the information be categorized?

Step 2: Review the Timeline by asking the following questions:

Do any of the events appear to occur too rapidly or too slowly to have reasonably occurred in the order or timing suggested by the data? (e.g. the letters and their postmarks).
Are there any underlying assumptions about the evidence that merit attention?
Does the case study contain any anomalous data or information that could be viewed as an outlier? What should be done about it?

 

Sample Solution

in visible-light irradiation is interested recently. Many visible light active photocatalysts that have good photocatalytic performance are CdS, CdSe, WO3, AgVO4, Bi2WO6, BiVO4, and etc [36]. Bismuth vanadate (BiVO4) is a low-cost semiconductor that has attracted special great attention for the organic pollutants degradation [37,38]. BiVO4 compounds have been prepared in three crystalline phases including monoclinic and tetragonal scheelite, and tetragonal zircon. Monoclinic form with the band gap~2.4 eV has the best photocatalytic performance in visible-light region [39-43]. Bismuth-based semiconductors have considered as the kinds of emerging and promising photocatalysts due to their unique crystal configurations and properties, and photo-induced charge carriers formation [44]. TiO2 coupled by BiVO4 is alternated as a way for enhancement of photocatalytic performance. BiVO4 due to its high visible-light absorption ability has been chosen as a sensitizer [45]. Absorption of a photon by semiconductors excites an electron [20] from the VB to the CB, if the photon energy (hv) equals or exceeds from the semiconductor/photocatalyst band gap. Simultaneously, a positive charge called a hole (h+) is also generated in the VB and resulted inthe formation of electron-hole pairs (Eq. (1)) [26]. Then these pairs (e-–h+ pair) move to the photocatalyst surface and in redox reactions with the adsorbed pollutants on the photocatalyst recombines, producing thermal energy or participate. The lifetime of an e-–h+ pair is very little [46] but is still enough for the promotion of redox reactions in the solution or gas phase in the semiconductor surface [26]. Then the photo-excited electrons react with molecular oxygen (O2) to the production of superoxide radical anions (•O2-) [47] (Eq. (2)), and the photo generated holes react with water to produce hydroxyl radicals (•OH) (Eq. (3)). Therefore, nanocomposites are enabled to have a powerful and durable photo-oxidation capability through generation of these strong radicals [48]. As these radicals are the main active species in the photo-oxidation process under visible light [49], they play crucial roles in the decomposition of the toxic and persistent organic pollutants (R) present at the surface of the photocatalyst and convert them into harmless species. The products due to the photodegradation are reduced to mineral compounds and finally CO2 and H2O are released (Eq. (4)) [50].
〖Photocatalyst〗_ □(→┴hν e^-+h^+ ) (1)
e^-+ O_2→ •O_2^- (2)

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