13,529 research outputs found
Pathological abelian groups: a friendly example
We show that the group of bounded sequences of elements of is an example of an abelian group with several well known, and not so well
known, pathological properties. It appears to be simpler than all previously
known examples for some of these properties, and at least simpler to describe
for others.Comment: 6 page
Visualizing curved spacetime
I present a way to visualize the concept of curved spacetime. The result is a
curved surface with local coordinate systems (Minkowski Systems) living on it,
giving the local directions of space and time. Relative to these systems,
special relativity holds. The method can be used to visualize gravitational
time dilation, the horizon of black holes, and cosmological models. The idea
underlying the illustrations is first to specify a field of timelike
four-velocities. Then, at every point, one performs a coordinate transformation
to a local Minkowski system comoving with the given four-velocity. In the local
system, the sign of the spatial part of the metric is flipped to create a new
metric of Euclidean signature. The new positive definite metric, called the
absolute metric, can be covariantly related to the original Lorentzian metric.
For the special case of a 2-dimensional original metric, the absolute metric
may be embedded in 3-dimensional Euclidean space as a curved surface.Comment: 15 pages, 20 figure
Mum. Dad. Do you need some help with that? Empowering older Australians in a digital era.
The change to a digital environment for Australian families is more than simply adopting internet connectivity or a mobile phone. Moving from an analog environment and into a digital sphere for many individuals is confronting: the transition requires digital media literacy, that is an understanding of devices, forms of connectivity, installation of devices and how best to use digital connectivity to connect with other family members. In this Australian study the interviewees revealed that tensions occur between middle and older adults as both generations try to understand the effect of the change to a digital environment on each other and navigate the best path that enables communication and connection between family members. This paper will primarily draw on the interviews held with middle adult John and his mother Vera
Infinitely many algebras derived equivalent to a block
We give a construction that in many cases gives a simple way to construct
infinite families of algebras that are not Morita equivalent, but are all
derived equivalent to the same block algebra of a finite group, and apply it to
some small blocks. We make some remarks relating this construction to Donovan's
Conjecture and Broue's Abelian Defect Group Conjecture
Equivalences of derived categories for symmetric algebras
We give a characterization of the sets of objects of the derived category of
a block of a finite group algebra (or other symmetric algebra) that occur as
the set of images of simple modules under an equivalence of derived categories.
We give some applications to proving that certain blocks have equivalent
derived categories
p-Adic Lifting Problems and Derived Equivalences
For two derived equivalent -algebras and , we
introduce a correspondence between \OO-orders reducing to and
\OO-orders reducing to . We outline how this may be used to
transfer properties like uniqueness (or non-existence) of a lift between
and . As an application, we look at tame algebras of
dihedral type with two simple modules, where, most notably, we are able to show
that among those algebras only the algebras and
can actually occur as basic algebras of blocks of
group rings of finite groups
The Test of Command: McNaughton and Exercise “Spartan,” 4–12 March 1943
The large-scale General Headquarters (GHQ) exercise known as “Spartan,” held in the south of England during March 1943, was a significant event in the history of the Canadian Army in the Second World War. The purpose of “Spartan” was to test the army in the dual tasks of breaking out of an established bridgehead and making the transition to open warfare. As a direct result of shortcomings on the exercise, three Canadian generals lost their commands. Of greatest significance was the eventual relief of General A.G.L. McNaughton as commander of the First Canadian Army in November 1943. During and after “Spartan” the Chief of the Imperial General Staff (CIGS), General Sir Francis Alan Brooke, and the Commander-in-Chief of Home Forces, General Sir Bernard Paget, claimed that McNaughton’s performance proved his incapacity to lead First Canadian Army in the field. In consequence, Brooke and Paget orchestrated his removal and Canadian military historians have generally supported their assessment. However, the considerable criticism directed at McNaughton resulting from “Spartan” has suffered from oversimplification. This article will review McNaughton’s performance during the exercise and assess its role in his relief
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