We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.
To send this article to your account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
An edge-coloured graph $G$ is called properly connected if any two vertices are connected by a properly coloured path. The proper connection number, $pc(G)$, of a graph $G$, is the smallest number of colours that are needed to colour $G$ such that it is properly connected. Let $\unicode[STIX]{x1D6FF}(n)$ denote the minimum value such that $pc(G)=2$ for any 2-connected incomplete graph $G$ of order $n$ with minimum degree at least $\unicode[STIX]{x1D6FF}(n)$. Brause et al. [‘Minimum degree conditions for the proper connection number of graphs’, Graphs Combin.33 (2017), 833–843] showed that $\unicode[STIX]{x1D6FF}(n)>n/42$. In this note, we show that $\unicode[STIX]{x1D6FF}(n)>n/36$.
We present several results on the connectivity of McKay quivers of finite-dimensional complex representations of finite groups, with no restriction on the faithfulness or self-duality of the representations. We give examples of McKay quivers, as well as quivers that cannot arise as McKay quivers, and discuss a necessary and sufficient condition for two finite groups to share a connected McKay quiver.
An undirected graph $G$ is determined by its $T$-gain spectrum (DTS) if every $T$-gain graph cospectral to $G$ is switching equivalent to $G$. We show that the complete graph $K_{n}$ and the graph $K_{n}-e$ obtained by deleting an edge from $K_{n}$ are DTS, the star $K_{1,n}$ is DTS if and only if $n\leq 2$, and an odd path $P_{2m+1}$ is not DTS if $m\geq 2$. We give an operation for constructing cospectral $T$-gain graphs and apply it to show that a tree of arbitrary order (at least $5$) is not DTS.
For a given set
$S\subseteq \mathbb {Z}_m$
and
$\overline {n}\in \mathbb {Z}_m$
, let
$R_S(\overline {n})$
denote the number of solutions of the equation
$\overline {n}=\overline {s}+\overline {s'}$
with ordered pairs
$(\overline {s},\overline {s'})\in S^2$
. We determine the structure of
$A,B\subseteq \mathbb {Z}_m$
with
$|(A\cup B)\setminus (A\cap B)|=m-2$
such that
$R_{A}(\overline {n})=R_{B}(\overline {n})$
for all
$\overline {n}\in \mathbb {Z}_m$
, where m is an even integer.
We examine a recursive sequence in which
$s_n$
is a literal description of what the binary expansion of the previous term
$s_{n-1}$
is not. By adapting a technique of Conway, we determine the limiting behaviour of
$\{s_n\}$
and dynamics of a related self-map of
$2^{\mathbb {N}}$
. Our main result is the existence and uniqueness of a pair of binary sequences, each the complement-description of the other. We also take every opportunity to make puns.
The notion of
$\theta $
-congruent numbers is a generalisation of congruent numbers where one considers triangles with an angle
$\theta $
such that
$\cos \theta $
is a rational number. In this paper we discuss a criterion for a natural number to be
$\theta $
-congruent over certain real number fields.
We study lower bounds of a general family of L-functions on the
$1$
-line. More precisely, we show that for any
$F(s)$
in this family, there exist arbitrarily large t such that
$F(1+it)\geq e^{\gamma _F} (\log _2 t + \log _3 t)^m + O(1)$
, where m is the order of the pole of
$F(s)$
at
$s=1$
. This is a generalisation of the result of Aistleitner, Munsch and Mahatab [‘Extreme values of the Riemann zeta function on the
$1$
-line’, Int. Math. Res. Not. IMRN2019(22) (2019), 6924–6932]. As a consequence, we get lower bounds for large values of Dedekind zeta-functions and Rankin-Selberg L-functions of the type
$L(s,f\times f)$
on the
$1$
-line.
We construct eta-quotient representations of two families of q-series involving the Rogers–Ramanujan continued fraction by establishing related recurrence relations. We also display how these eta-quotient representations can be utilised to dissect certain q-series identities.
We introduce the notion of the slot length of a family of matrices over an arbitrary field
${\mathbb {F}}$
. Using this definition it is shown that, if
$n\ge 5$
and A and B are
$n\times n$
complex matrices with A unicellular and the pair
$\{A,B\}$
irreducible, the slot length s of
$\{A,B\}$
satisfies
$2\le s\le n-1$
, where both inequalities are sharp, for every n. It is conjectured that the slot length of any irreducible pair of
$n\times n$
matrices, where
$n\ge 5$
, is at most
$n-1$
. The slot length of a family of rank-one complex matrices can be equal to n.
Isaacs and Seitz conjectured that the derived length of a finite solvable group $G$ is bounded by the cardinality of the set of all irreducible character degrees of $G$. We prove that the conjecture holds for $G$ if the degrees of nonlinear monolithic characters of $G$ having the same kernels are distinct. Also, we show that the conjecture is true when $G$ has at most three nonlinear monolithic characters. We give some sufficient conditions for the inequality related to monolithic characters or real-valued irreducible characters of $G$ when the commutator subgroup of $G$ is supersolvable.
The notion of recurrent fractal interpolation functions (RFIFs) was introduced by Barnsley et al. [‘Recurrent iterated function systems’, Constr. Approx.5 (1989), 362–378]. Roughly speaking, the graph of an RFIF is the invariant set of a recurrent iterated function system on
$\mathbb {R}^2$
. We generalise the definition of RFIFs so that iterated functions in the recurrent system need not be contractive with respect to the first variable. We obtain the box dimensions of all self-affine RFIFs in this general setting.
For
$n\geq 3$
, let
$Q_n\subset \mathbb {C}$
be an arbitrary regular n-sided polygon. We prove that the Cauchy transform
$F_{Q_n}$
of the normalised two-dimensional Lebesgue measure on
$Q_n$
is univalent and starlike but not convex in
$\widehat {\mathbb {C}}\setminus Q_n$
.
By making use of the ‘creative microscoping’ method, Guo and Zudilin [‘Dwork-type supercongruences through a creative $q$-microscope’, Preprint, 2020, arXiv:2001.02311] proved several Dwork-type supercongruences, including some conjectures of Swisher. In this paper, we apply the Guo–Zudilin method to prove a new Dwork-type supercongruence, which uniformly generalises several conjectures of Swisher.
Let E and D be open subsets of
$\mathbb {R}^{n+1}$
such that
$\overline {D}$
is a compact subset of E, and let v be a supertemperature on E. A temperature u on D is called extendable by v if there is a supertemperature w on E such that
$w=u$
on D and
$w=v$
on
$E\backslash \overline D$
. From earlier work of N. A. Watson, [‘Extendable temperatures’, Bull. Aust. Math. Soc.100 (2019), 297–303], either there is a unique temperature extendable by v, or there are infinitely many; a necessary condition for uniqueness is that the generalised solution of the Dirichlet problem on D corresponding to the restriction of v to
$\partial _eD$
is equal to the greatest thermic minorant of v on D. In this paper we first give a condition for nonuniqueness and an example to show that this necessary condition is not sufficient. We then give a uniqueness theorem involving the thermal and cothermal fine topologies and deduce a corollary involving only parabolic and coparabolic tusks.
Suppose that
$\mathcal {A}$
is a unital subhomogeneous C*-algebra. We show that every central sequence in
$\mathcal {A}$
is hypercentral if and only if every pointwise limit of a sequence of irreducible representations is multiplicity free. We also show that every central sequence in
$\mathcal {A}$
is trivial if and only if every pointwise limit of irreducible representations is irreducible. Finally, we give a nice representation of the latter algebras.
Urysohn’s lemma is a crucial property of normal spaces that deals with separation of closed sets by continuous functions. It is also a fundamental ingredient in proving the Tietze extension theorem, another property of normal spaces that deals with the existence of extensions of continuous functions. Using the Cantor function, we give alternative proofs for Urysohn’s lemma and the Tietze extension theorem.