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Abstract: Disaster associated with natural hazards can lead to important changes—positive or negative—in socio-ecological systems. When disasters occur, much attention is given to the direct disaster impacts as well as relief and recovery operations. Although this focus is important, it is noteworthy that there has been little research on the characteristics and progress of change induced by disasters. Change, as distinct from impacts, encompasses formal and informal responses to disaster events and their direct and indirect impacts. While smaller disasters do not often lead to significant changes in societies and organizational structures, major disasters have the potential to change dominant ways of thinking and acting. Against this background, the article presents an analytical framework for distinguishing change from disaster impacts. Drawing from research in Sri Lanka and Indonesia, formal and informal changes after the Indian Ocean Tsunami of 2004 are examined and discussed against the background of the conceptual framework. The changes examined range from the commencement of the peace process in Aceh, Indonesia, to organizational and legal reforms in Sri Lanka. The article concludes that change-making processes after disasters need to be understood more in depth in order to derive important strategic policy and methodological lessons learned for the future, particularly in view of the increasing complexity and uncertainty in decision making due to climate change.

Using the HEXTE experiment on-board the RXTE satellite, we performed a search for hard X-ray tails in Sco X-1 spectra. We found strong evidence for the presence of such a non-thermal component on several occasions. Using the PCA/ RXTE we were able to track the position of the source along the Z diagram, and we observed that the presence of the hard X-ray tail is not confined to a particular region. However, we found a correlation between the power law index of the non-thermal component and the position of the source in the Z diagram, suggesting that the hard X-ray spectrum (i.e., E > 50 keV) becomes flatter as the mass accretion rate increases. We were also able to study the temporal variation of the appearance/absence of the hard X-ray component. With our derived luminosities, we were also able to test the idea that X-ray luminosities can be used to distinguish between X-ray binary systems containing neutron stars and black holes.

Summary Thepositive half A+ of an ordered abelian groupA is the set {x ∈ A∣x ⩾ 0} andM A+ is amodule if for allx, y ∈ M alsox + y, |x − y| ∈M. Ifθ ∈ A+\M thenM(θ) is the module generated byM andθ. S M isunbounded inM if(∀x ∈ M)(∃y ∈ S)(x ⩽ y) and isdense inM if (∀x1, x2 ∈M)(∃y ∈ S) (x1 < x2 ℂ x1 ⩾ y ⩾ x2). IfM is a module, or a subgroup of any abelian group, a real-valuedg: M → R issubadditive ifg(x + y) ⩽ g(x) + g(y) for allx, y ∈ M. The following hold:(1)IfM andM* are modules inA andM M* A+ then a subadditiveg:M → R can always be extended to a subadditive functionF:M*→ R when card(M) = ℵ0 and card(M*) ⩽ ℵ1, or wheneverM* possesses a countable dense subset.(2)IfZ A is a subgroup (whereZ denotes the integers) andg:Z+→ R is subadditive with g(n)/n = − ∞ theng cannot be subadditively extended toA+ whenA does not contain an unbounded subset of cardinality .(3)Assuming the Continuum Hypothesis, there is an ordered abelian groupA of cardinality ℵ1 with a moduleM and elementθ∈A+/M for whichA+= M(θ), and a subadditiveg:M → R which does not extend toA+. This even happens withg ⩾ 0.(4)Letg:A+→ R be subadditive on the positive halfA+ ofA. Then the necessary and sufficient condition forg to admit a subadditive extension to the whole groupA is: sup{g(x + y) − g(x)∣x⩾ −y} < + ∞ for eachy < 0 inA.(5)IfM is a subgroup of any abelian groupA andg:M → K is subadditive, whereK is an ordered abelian group, theng admits a subadditive extensionF:A → K.(6)IfA is any abelian group andg:A → R is subadditive, theng = λ + ϕ whereλ:A → R is additive andϕ ⩾ 0 is a non-negative subadditive functionϕ:A → R. IfA is aQ-vector spaceλ may be takenQ-linear.(7)Ifg:V → R is a continuous subadditive function on the real topological linear spaceV then there exists a continuous linear functionalλ:V → R and a continuous subadditiveϕ:V → R such thatg = λ + ϕ andϕ ⩾ 0. ifV = Rn this holds for measurable subadditiveg with a continuousλ and measurableϕ.

A Stein groupoid (quasigroup) is a groupoid (quasigroup) satisfying the identityx(xy)=yx. We show that, for certain two variable identities, the variety of Stein groupoids defined by any one of these identities has the properties that every groupoid in the variety is a quasigroup and that the free groupoid generated by two elements is of finite (small) order which we determine. These results provide characterizations of some Stein quasigroups of small order and we give some further characterizations involving other identities.

The recursive minimization problem\[ f ( n ) = \min \left\{ \sum^r_{i = 1} f ( a_i ) \right\} + g ( n ), \] where the minimum is taken over all r-tuples $a = ( a_1 , \cdots ,a_r )$ of integers $a_i $, such that $0\leqq a_i < n$, $1\leqq i\leqq r$, $\sum^r_{i = 1} a_i = n$, is studied. Necessary and sufficient conditions on $g( n )$, satisfied by many nonnegative convex sequences, are found for the solution to be given by the recurrence relation \[f ( n ) = \sum_{i = 1}^r f \left( \left[ \frac{n + i - 1}{r} \right] \right) + g ( n ).\] A similar recurrence relation is found for the solution when gsatisfies certain concavity conditions.

The High Energy X-Ray Timing Experiment (HEXTE) is one of three scientific instruments aboard the RossiX-RayTimingExplorer(RXTE), which was launched on 1995 December 30. RXTEperforms timing and spectral studies of bright X-ray sources to determine the physical parameters of these systems. The HEXTE consists of two independent clusters of detectors, each cluster containing four NaI(Tl)/CsI(Na) phoswich scintillation counters sharing a common 1° FWHM field of view. The field of view of each cluster is switched on and off source to provide near real-time background measurements. The net open area of the eight detectors is 1600 cm2, and each detector covers the energy range 15-250 keV with an average energy resolution of 15.4% at 60 keV. The in-flight performance of the HEXTE is described, the light curve and spectrum of the Crab Nebula/pulsar is given, and the 15-240 keV spectrum of the weak source, active galaxy MCG +8-11-11 is presented to demonstrate the weak source spectral capabilities of HEXTE.

The UCSD, WU, UCR and Nova collaboration has made significant progress on the necessary techniques for coded mask imaging of gamma-ray bursts: position sensitive CZT detectors with good energy resolution, ASIC readout, coded mask imaging, and background properties at balloon altitudes. Results on coded mask imaging techniques appropriate for wide field imaging and localization of gamma-ray bursts are presented, including a shadowgram and deconvolved image taken with a prototype detector/ASIC and MURA mask.