Articles / Άρθρα

The reaction of [Mn(O2CMe)2] · 4H2O with pdH2 (1,3-propanediol) or mpdH2 (2-methyl-1,3-propanediol) in the presence of NaN3 in MeCN/py (py = pyridine) results in the formation of two new one-dimensional coordination polymers composed of a [MnIII 6MnII 11(μ4-O)8(μ3-N3)4]25+ octahedral unit. The peripheral ligation is completed by pd2- (or mpd2-), acetate, pyridine and μ-1,3-N3 - ligands. The latter bridges each Mn17 unit to its neighboring one, resulting in the formation of the two 1-D coordination polymers. Variable-temperature dc magnetic susceptibility studies indicate the existence of predominantly ferromagnetic interactions and a resulting giant ground state spin within the Mn17 units and intermolecular antiferromagnetic exchange interactions between the neighboring Mn17 units that result in diamagnetic ground spin states for both polymeric compounds.

The crystal structure of the title compound, C9H 12O4S, was determined in order to investigate the effect of the eclipsed O atoms on the bond length of the vicinal quaternary C atoms. The two quaternary C atoms of the noradamantane skeleton and the two O atoms to which they are connected all located essentially in the same plane (maximum deviation = 0.01 Å), resulting in an eclipsed conformation of the C - O bonds. The C - C bond of the quaternary C atoms is 1.581 (3) Å, considerably longer than the other C - C bonds of the molecule due to the stretch of the cage structure.

The title compound, C18H24I2, has an adamantanoid structure with tetra-hedral cages having four C atoms lying on the same plane [(I-)C-C-C-C(-I) torsion angle = 0°]. The plane is extended by the two I atoms, each having a deviation of 1.0 (6) Å [C-C-C-I torsion angle = 178.9 (4)°]. The central C-C bond connecting the two quaternary carbons seems enlarged [1.593 (9) Å] in comparison to the corresponding bond in [2]diadamantane [1.554 (3) Å]. This is attributed to the presence of the electronegative I atoms, which affect inductively the C atoms of the four-C-atom plane, making the central C-C bond weaker.

Stille coupling of 3,5-bis(5-bromothien-2-yl)-4H-1,2,6-thiadiazin-4-one (10) with 2-(tri-n-butylstannyl)thiazole and Pd(Ph 3 P) 2 Cl 2 in PhMe, at ca. 110 ◦ C, for 2 h, gave 3,5-bis[5-(thiazol-2-yl)thien-2-yl]-4H-1,2,6-thiadiazin-4-one (9) in 81% yield. The latter is evaluated for its electronic properties.

Stille coupling of 5-chloro-4-oxo-4H-1,2,6-thiadiazin-3-yl trifluoromethanesulfonate (7) with tributyl(3-n-hexylthien-2-yl)stannane and Pd(Ph 3 P) 2 Cl 2 in PhMe at ca. 20 ◦ C, for 24 h gave 3-chloro-5-(3-n-hexylthien-2-yl)-4H-1,2,6-thiadiazin-4-one (9) with a 60% yield. The latter is a potentially useful building block for the synthesis of oligomeric and polymeric donors for organic photovoltaics.

Stille coupling of 5,5'-dichloro-4H,4‘H-[3,3'-bi(1,2,6-thiadiazine)]-4,4'-dione (8) with 9-decyl-3-[5-(tributylstannyl)thien-2-yl]-9H-carbazole and Pd(Ph3P)2Cl2 in PhMe, at ca. 110 °C, for 2 h, gave 5,5'-bis[5-(9-decyl-9H-carbazol-3-yl)thien-2-yl]-4H,4‘H-[3,3'-bi(1,2,6-thiadiazine)]-4,4'-dione (7) in 51% yield. The latter is investigated as an oligomer donor for organic photovoltaics.

Small island states, due to their size, remoteness and dependence on foreign capital, are often susceptible to various global disruptions and crises. The effects of such crises can be chaotic, seriously damaging their economies and altering their systems. However, in the context of tourism crisis management, linear approaches are predominant overlooking the chaotic characteristics and transformations of the complex tourism system. In response, this research investigates the implications of the economic crisis and the interaction effects of unforeseen events, on Cypriot tourism through a chaos theory perspective. Based on semi-structured interviews, archival document analysis and a pertinent literature review, findings indicate that the evolution of Cyprus tourism was not a linear process, but instead iterative, characterised by interactions of several endogenous and exogenous events that have shaped its systemic transformation. The research reveals the lack of comprehensive policy responses to crises that would enable the sustainable tourism development of Cyprus. The paper concludes that it is imperative for small island states to understand holistically the interrelated dimensions of crises and therefore mitigate their detrimental consequences. To this end, tourism policy needs to realise that crises and sustainability are not linear processes but evolving systemic configurations that necessitate the preparedness of tourism policy-makers and stakeholders to anticipate change and swiftly respond.

This paper focuses on coexistence and self-coexistence challenges between secondary heterogeneous wireless networks/users sharing TV Whitespace spectrum. The coexistence problems arise from having several primary and secondary networks of different technologies cohabiting the same licensed spectrum simultaneously. The self-coexistence problems arise from many secondary systems /users coexisting at the same place while using identical or different technologies. In particular, fair distribution of available spectrum becomes a serious issue. In this paper, we use a game theoretic approach to model the self-coexistence problem as a competitive game between secondary networks. We show that our game belongs to the class of congestion-averse games which are known to possess pure Nash equilibria. This leads us to a decentralized approach for spectrum sharing among systems with different PHY/MAC characteristics. We show that our proposal outperforms other centralized algorithms in terms of user fairness and per-user theoretical data rates.

This study investigated whether switching from a diet rich in saturated fatty acids (SAFAs) to a diet rich in monounsaturated fatty acids (MUFAs) or to one with equal amounts of MUFAs-SAFAs favorably affects the lipid profile of hypercholesterolemic mice. C57BL/6 mice (n = 82) were allocated into 4 groups. The first group (control, n = 10) was fed standard chow. The 3 remaining groups (n = 24 mice/group) were fed a SAFA-rich diet for 8 weeks and were then allocated for 16 weeks to either a MUFA-rich diet, an equal in MUFAs-SAFAs-rich diet, or continued the previous SAFA-rich diet. After 8 weeks, mice consuming SAFA-rich diet had increased weight, total cholesterol (TC), and high-density lipoprotein cholesterol (HDL-C) levels (P <.05 vs baseline). At week 24, MUFA-rich and MUFA-SAFA rich diets decreased TC and low-density lipoprotein cholesterol (LDL-C) levels (P <.05) compared with week 8. In conclusion, switching to MUFA-rich diets or substituting half of the SAFAs with MUFAs can reverse diet-induced-hypercholesterolemia.

Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 1052 erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.

(Figure Presented) Singles networks: The use of 1,3-propanediol and of 2-methyl-1,3-propanediol in manganese carboxylate chemistry leads to two new 3D coordination polymers with an unprecedented Mn19 repeating unit. The polymers have open framework structures with nanometer-sized cavities (see picture; Na not visible, Mn blue, O red, C gray). The Mn19 units have a ground spin state of S = 23/2 and behave as single-molecule magnets.

We present follow-up observations of the far-infrared (FIR) sources at 90, 150 and 180 μm detected as part of the ISOPHOT EBL project, which has recently measured the absolute surface brightness of the cosmic infrared background (CIRB) radiation for the first time independently from COBE data. We have observed the fields at the North Galactic Pole region in the optical and near-IR, and complement these data with Sloan Digital Sky Survey photometry, and spectroscopy where available, and present identifications of the 25 FIR sources which reach down to ∼150 mJy in all three ISOPHOT bands. Identifications are done by means of full spectral energy density fitting to all sources in the FIR error circle areas. Approximately 80 per cent are identified as star-forming or star-bursting galaxies at z < 0.3. We also find that more than half of the counterparts have disturbed morphologies, with signs of past or present interactions. However, only 20 per cent of all the sources are uniquely matched with a single galaxy -40 per cent are blends of two or more of these nearby star-forming galaxies, while another 20 per cent are likely blends of nearby and fainter galaxies. The final 20 per cent are likely to be more luminous IR galaxies at higher redshifts. The blended sources have an effect on the FIR source counts. In particular, taking into account realistic confusion or blending of sources, the differential FIR counts move down by a factor of ∼1.5 and steepen in the 100 to 400 mJy range.

Consider a network vulnerable to viral infection, where the security software can guarantee safety only to a limited part of it. We model this practical network scenario as a non-cooperative multi-player game on a graph, with two kinds of players, a set of attackers and a protector player, representing the viruses and the system security software, respectively. We are interested in the associated Nash equilibria, where no network entity can unilaterally improve its local objective. We obtain the following results: For certain families of graphs, mixed Nash equilibria can be computed in polynomially time. These families include, among others, regular graphs, graphs with perfect matchings and trees. The corresponding price of anarchy for any mixed Nash equilibria of the game is upper and lower bounded by a linear function of the number of vertices of the graph. (We define the price of anarchy to reflect the utility of the protector). Finally, we introduce a generalised version of the game. We show that the existence problem of pure Nash equilibria here is NP-complete.

The problem of identifying machine cells and corresponding part families in cellular manufacturing has been extensively researched over the last thirty years. However, the complexity of the problem and the considerable number of issues involved in its solution create the need for increasingly efficient algorithms. In this paper the use of genetic programming for the solution of a simple version of the problem is investigated. The methodology is tested on a number of problems taken from the literature and comparative results are presented.

A large [Mn10Na]4 loop-of-loops aggregate was prepared from the use of 1,3-propanediol (pdH2) in manganese carboxylate chemistry. It is constructed from four [Mn10(μ 3-O)2(O2CMe)13(pd) 6(py)2]- loops linked through Na+ ions and exhibits a saddlelike topology. Magnetic characterization showed that the Mn10 loop has an S ∼ 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase alternating current signals and also hysteresis loops that, however, are not typical of single-molecule magnets because of the existence of intermolecular interactions between the Mn 10 units.

Invited for the cover of this issue is Anastasios Tasiopoulos from the University of Cyprus. The cover image shows photos from the southwestern Cyclades island group of the Aegean Sea, which contain a wealth of minerals and rocks. Some of these exhibit porous structures and interesting magnetic properties.

The synthesis and characterization of {[Co9(INA)18(H2O)6]·11DMF·15H2O}∞ (Co9-INA·11DMF·15H2O) (INA- = the anion of isonicotinic acid) is reported. It exhibits a rigid 3D-porous structure with a Co9 repeating unit consisting of four [CoII2(μ-O2CR)2(μ-H2O)] subunits (two unique) linked through bridging INA- ligands to an isolated CoII ion (half unique). The [CoII2] dimers and the isolated CoII ion have assembled to create a trinodal (6,7,8)-coordinated network with point symbol (32.411.56.62)2(32.418.54.64)2(34.44.54.63). Gas sorption studies revealed that Co9-INA exhibits 910 m2 g-1 BET area, 4.2 mmol g-1 CO2 uptake at 273 K/1 bar, and 6.7 CO2/CH4 selectivity at zero coverage. Furthermore, Co9-INA displays capability for exchange of the guest solvent molecules by various organic molecules in a single-crystal to single-crystal fashion. Direct and alternating current magnetic susceptibility studies revealed the existence of dominant antiferromagnetic interactions between the Co2+ ions that result in a paramagnetic ST = 3/2 spin ground state value. Overall, this work emphasizes the potential of relatively simple and inexpensive polytopic ligands, such as isonicotic acid, to stabilize microporous MOFs with significant CO2 sorption capacity.

A new Cu2+ complex that was isolated from the initial use of 5-((pyridin-4-ylmethylene)amino)isophthalic acid (PEIPH2) in 3d metal-organic framework (MOF) chemistry is reported. Complex {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞ denoted as Cu-PEIP·7DMF was isolated from the reaction of Cu(NO3)2·2.5H2O with PEIPH2 in N,N-dimethylformamide (DMF) at 100 °C and contains both the PEIP2- ligand and its 5-NH2-mBDC2- fragment. After the structure and properties of Cu-PEIP were known an analogous complex was prepared by a rational synthetic method that involved the reaction of Cu(NO3)2·2.5H2O, 5-((pyridin-4-ylmethyl)amino)isophthalic acid (PIPH2-the reduced analogue of PEIPH2) and 5-NH2-mBDCH2 in DMF at 100 °C. Cu-PEIP comprises two paddle-wheel [Cu2(COO)4] units and exhibits a 3D-framework with a unique trinodal underlying network and point symbol (4.52)4(42·54·64·83·92)2(52·84). This network consists of pillared kgm-a layers containing a hexagonal shaped cavity with a relatively large diameter of ∼8-9 Å surrounded by six trigonal shaped ones with a smaller diameter of ∼4-5 Å and thus resembles the structure of HKUST-1. Gas sorption studies revealed that Cu-PEIP exhibits a 1785 m2 g-1 BET area as well as high CO2 sorption capacity (4.75 mmol g-1 at 273 K) and CO2/CH4 selectivity (8.5 at zero coverage and 273 K).

The missing VIV11VV7 oxidation-state member of the polyoxooctadecavanadate(IV/V) - azide family of inorganic host-guest systems has been incorporated in a NaI-containing 3D architecture; the complex shows remarkable inhibition properties on human platelet aggregation and antitumoural activity against cancer cell lines

The initial use of 1,3-propanediol in mixed Mn/3d cluster chemistry has led to a Mn III 28Mn II 8Ni II 4 molecular aggregate which consists of two Mn III 8Ni 2 loops and two Mn III 6Mn II 4 supertetrahedral units and displays a high ground spin state value S T = 26 ± 1.