Persistent supersolid phase of hard-core bosons on the triangular lattice

We study hard-core bosons with unfrustrated hopping ($t$) and nearest neighbour repulsion ($U$) on the triangular lattice. At half-filling, the system undergoes a zero temperature ($T$) quantum phase transition from a superfluid phase at small $U$ to a supersolid at $U_c \approx 4.45$ in units of $2t$. This supersolid phase breaks the lattice translation symmetry in a characteristic $\sqrt{3} \times \sqrt{3}$ pattern, and is remarkably stable--indeed, a smooth extrapolation of our results indicates that the supersolid phase persists for arbitrarily large $U/t$.Comment: 4 pages, 5 figures, two column forma

Supersolid Order from Disorder: Hard-Core Bosons on the Triangular Lattice

We study the interplay of Mott localization, geometric frustration, and superfluidity for hard-core bosons with nearest-neighbor repulsion on the triangular lattice. For this model at half-filling, we demonstrate that superfluidity survives for arbitrarily large repulsion, and that diagonal solid order emerges in the strongly correlated regime from an order-by-disorder mechanism. This is thus an unusual example of a stable supersolid phase of hard-core lattice bosons at a commensurate filling.Comment: 4 pages, 2 figures; finite-size scaling discussion adde

Modelling Clock Synchronization in the Chess gMAC WSN Protocol

We present a detailled timed automata model of the clock synchronization algorithm that is currently being used in a wireless sensor network (WSN) that has been developed by the Dutch company Chess. Using the Uppaal model checker, we establish that in certain cases a static, fully synchronized network may eventually become unsynchronized if the current algorithm is used, even in a setting with infinitesimal clock drifts

U–Pb zircon geochronology, petrochemical and Sr–Nd isotopic characteristic of Late Neoproterozoic granitoids of the Bornaward complex (Bardaskan-NE Iran)

The Bornaward granitoids in the Taknar zone are located in the northeast of the central Iranian block in northeast Iran (Khorasan Razavi province), about 280 km southwest of Mashhad city and 28 km northwest of Bardaskan city. Taknar zone is an exotic block, bordered by two major faults, the Great Kavir fault in the south and Rivash fault in the north. Intrusive rocks of the study area, called the Bornaward granitoid complex (BGC), include of granite, alkali granite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite, diorite and gabbro intruded into the center of Taknar zone. These intrusive rocks affected low grade metamorphism. The results of U-Pb zircon dating on two granite samples, one belonging to the Taknar mine west of the study area and the other the Bornaward granitoids in the eastern part of study area, and also one granodiorite the Taknar mine area and one diorite the Bornaward area, yield ages of the granites as 540.5±2.9 Ma (Taknar mine area) and 550.41 3.21,-4.54 Ma (Bornaward area), the granodiorite as 550±6.9 Ma and diorite as 551.96±4.32 Ma, all Late Neoproterozoic. The Bornaward intrusive bodies are classified as belonging to the ilmenite-series of reduced granitoids. Some small high magnetite-granite and tonalite outcrops in the study area are classified as belonging to the magnetite-series of oxidized granitoids. Chemically, most granitoids of the study area are S-type middle-high metaluminous to slightlymiddle peraluminous and belong to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichments in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) elements and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REEs) plots indicate minor enrichments of LREEs in comparison with HREEs, with (La/Yb)N between 1.04 -7.90 and total of REEs of the samples between 44.8 ppm (minimum) and 293.5 ppm (maximum) with strong negative anomaly of Eu compared to other Rare Earth elements. The Bornaward granitoid have an initial 87Sr/86Sr and 143Nd/144Nd ranging 0.703514 to 0.716888 and 0.511585 to 0.512061, respectively, when recalculated to an age of 550 to 538 Ma, consistent with the new radiometric age results. Initial εNd isotope values for granite, granodiorite and diorite range -6.73 to 2.52. TDM age of the BGC is 1.08-1.70 Ga. This indicates that the Bornaward granitoid complex (BGC) derived partial melting of distinct basement source regions with very high initial 87Sr/86Sr and underwent extensive crustal contamination

Studies of bosons in optical lattices in a harmonic potential

We present a theoretical study of bose condensation and specific heat of non-interacting bosons in finite lattices in harmonic potentials in one, two, and three dimensions. We numerically diagonalize the Hamiltonian to obtain the energy levels of the systems. Using the energy levels thus obtained, we investigate the temperature dependence, dimensionality effects, lattice size dependence, and evolution to the bulk limit of the condensate fraction and the specific heat. Some preliminary results on the specific heat of fermions in optical lattices are also presented. The results obtained are contextualized within the current experimental and theoretical scenario.Comment: Revised version, References updated, a new section on Fermions added, 14 pages, 16 figure

Correlated electrons in the presence of disorder

Several new aspects of the subtle interplay between electronic correlations and disorder are reviewed. First, the dynamical mean-field theory (DMFT)together with the geometrically averaged ("typical") local density of states is employed to compute the ground state phase diagram of the Anderson-Hubbard model at half-filling. This non-perturbative approach is sensitive to Anderson localization on the one-particle level and hence can detect correlated metallic, Mott insulating and Anderson insulating phases and can also describe the competition between Anderson localization and antiferromagnetism. Second, we investigate the effect of binary alloy disorder on ferromagnetism in materials with $f$-electrons described by the periodic Anderson model. A drastic enhancement of the Curie temperature $T_c$ caused by an increase of the local $f$-moments in the presence of disordered conduction electrons is discovered and explained.Comment: 17 pages, 7 figures, final version, typos corrected, references updated, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

Geochronology, Petrology and Geochemistry of Intermediate and Mafic Rocks of Bornaward Plutonic Complex (Northwest Bardaskan, Iran)

The study area is located in the northeast of Iran (the Khorasan Razavi province) and 28 km northwest of Bardaskan city and in position of 57˚ 46΄ to 57˚ 52΄ latitude and 35˚ 21΄ to 35˚ 24΄ longitude. The study area is a part of Taknar zone. The Taknar geological-structural zone is situated in the north Central Iranian microcontinental and it is a part of Lut block (Fig.1). Taknar plutonic complex that is situated in the Taknar structural zone is located in the northern part of Iranian microcontinent. Chemical analysis of REE and minor elements of samples of the Bornaward diorites and gabbro’s took place in the ACME Lab. in Vancouver, Canada, by the ICP-MS method (Table. 1). For the Bornaward diorite dating by the U-Pb method, zircon grains of material remaining in the sieve, Bromoform were isolated from light minerals by cleaning and were isolated with a minimum size of 25 microns, and then studies took place in the Crohn's Laser Lab Arizona (Gehrels et al., 2008). Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Nd)i , (87Sr/86Sr)i ratios and ƐNd (T=552), ƐNd (T=0), ƐSr (T=552) and ƐSr (T=0) took place in radioisotope Laboratory, University of Aveiro in Portugal. Geology of study area The study area forms the central part of the Bornaward plutonic complex. This complex is a granitoid assemblage including granite, granodiorite, tonalite and granophyre. The central part has been formed by intermediate and basic intrusive rocks such as diorite, quartz diorite and gabbro units (Fig. 2). From the genetic point of view, the intermediate and mafic rocks of the Taknar plutonic complex does not have any relationship with granitoid rocks of this assemblage, and they are related to a similar magmatic phase but are separated from this granitoid assemblage. However, these mafic and intermediate units are older than granitic units at the rim of the complex that are called Bornaward granite. The main minerals in the diorite and quartz diorite rocks are plagioclase and hornblende and we can see biotite in the quartz dioritic rocks. Quartz exists as tiny grains and anhedral and in the matrix rock. The amount of Quartz in the quartz diorites is 5 to 20%. Plagioclases usually have normal zoning and are highly altered to sericite. Most of the plagioclases were saussuritized. Altered minerals resulted from plagioclase and hornblende are sericite, epidote, chlorite, zoisite and clinozoisite.The main minerals in the gabbro are pyroxene, hornblende, and fine grains plagioclase. Minor minerals in the rocks are apatite, magnetite and other opaque. The main texture of intermediate and mafic rocks in this assemblage is medium granular to coarse grain and especially in the intermediate rocks and gabbro rocks, we can see scattered poikilitic, intersertal, sub-ophitic and porphyroid texture. The area diorite and gabbro is located locate in Tholeiitic and Calc-alkaline series (Fig. 9). Shand index (Al2O3/(CaO+Na2O+K2O)) is obtained under 1.1, in Metaluminous field (Fig. 7) and I-type granite field (Chappell and White, 2001). Based on the TAS diagram (Middlemost, 1985), all the diorite and gabbro samples are located in diorite, gabbro-diorite and gabbro-norite groups (Fig. 6). The diorite and gabbro show enrichment LREE and low ascending pattern ((La/Yb)N =1.40-6.12 and LaN =12.26-75.81). Measurement of U-Th-Pb isotopes of the Bornaward diorite zircons of BKCh-03 sample (Table 2) show that its age is related to 551.96±4.32 Ma ago (Upper Precambrian (Neoproterozoic) (Ediacaran). The (87Sr/86Sr)i and (143Nd/144Nd)i content of Bornaward diorite and gabbro rocks is located in the range of 0.7038 to 0.7135 and 0.51203 to 0.51214, respectively (Tables 3 and 4). It shows that the diorite and gabbro rocks can be affected by hydrothermal alteration because their (87Sr/86Sr)i is above (Fig. 16). The numeral amounts of ƐNd(T=552) of Bornaward diorite and gabbro are 2.0 to 4.0. The Bornaward diorite and gabbro rocks show a widespread enriched pattern of Rb, U, K, Pb, La and Th elements than chondrite, while Ba, Ti, Ta, Sr and Nb elements show reduction as a result of fractional crystallization (Fig. 11). The rocks of this complex are formed at the continental margin and VAG environment (Fig. 18) which is related to the subduction of the oceanic crust that exists between the Iranian microcontinent and the Afghan Block. This assemblage with age of Late Neoproterozoic is the result of extensive magmatism in the northern part of the Iranian microcontinent due to Katangahi orogeny event. The similar magmatism in the northern part of the Iranian microcontinent is existing as Khaf-Kashmar-Bardeskan volcanoplutonic belt. Based on the geochemical investigations, the magmatism of these rocks has been tholeiitic and calk-alkaline and have formed the coexistent rocks with I-type granites. Alumina saturation index for intermediate and mafic rocks of Bornaward complex is metalumina. These are medium-K rocks and enriched in the LILE such as Rb, Pb, U and Th while depleted of the Nb, Ti, Ta, Sr and Ba. Therefore, it shows that these rocks have resulted from the mixing by the lower crust. The low (87Sr/86Sr)i Bornaward diorite and gabbro rocks and the numeral amounts of Ɛ0Nd(present) of these rocks from -0.2 to 4.0 show that production of such intrusive masses can be attributed to the source of upper mantle or contaminated lower continental crust. Environment of formation of the intermediate and basic rocks of the Bornaward plutonic complex is active continental margin and volcanic arc environment.کمپلکس پلوتونیک برنورد واقع در زون ساختاري تکنار، در شمال خرد قاره ایران مرکزي و د ر 20 کیلومتري شما لغر ب شهرستان بردسکن قرار دارد. این مجموعه با سنی معادل اواخر پرکامبرین (نئوپروتروزوئیک)، نتیجه فعالیت ماگمایی وس یع شمال خرد قاره ایران مرکزي در اثر پدیده کوهزایی کاتانگاهی است. مشابه این ماگماتیسم در شمال خرد قاره ایران مرکزي بهصورت کمربند ولکانو- پلوتونیک خواف- کاشمر- بردسکن همچون گرانیتوئیدهاي کاشمر وجود دارد. این کمپلکس بزرگمقیاس در واقع مجموع هاي گرانیتوئید ي شامل سنگهاي گرانیت ی، گرانودیوری تی، تونالی تی و گرانوفی ري است که بخ ش مرکزي آن از ی ک گرو ه واحدهاي گابرویی، دیوریت ی و کوارتزدیوریتی تشکیلشده است. بافت اصلی این سن گهاي حدواسط و مافی ک، گرانولار متوسط تا درش تبلور اس ت و باف تهاي پورفیروئید بهویژه در سنگهاي حدواسط و بافتهاي پوئیکلیتیک و سابافیتیک در سن گهاي گابرویی ب هصورت پراکنده به چشم میخورد. کانی اصلی فرومنیزیندار سنگهاي مافیک و حدواسط، کانی هورنبلند است و در نمونههاي کوارتزدیوریتی، بیوتیت نیز دیده میشود. سنگهاي حدواسط و مافیک کمپلکس پلوتونیک برنورد از لحاظ ژنتیکی با سنگهاي گرانیتوئیدي این مجموعه ارتباطی مستقیم دارند. از لحاظ ارتباط صحرایی و بررسیهاي سنی چنین مشخص میشود که این واحدهاي مافیک و حدواسط نسبت به واحد گرانیتی و دیگر واحدهاي نفوذي اسیدي این کمپلکس قدیمیتر بوده و توسط این واحدها قطع شدهاند. 551 میلی ون /96 ±4/ سن این توده هاي نفوذي 32 ،U-Pb بر اساس سنسنجی دیوریتهاي منطقه برنورد با استفاده از کانی زیرکن بهروش سال قبل (اواخر پرکامبرین) بهدست آمده اس ت. بر پایه بررس یها ي ژئوشیمیایی، تحولات ماگمایی این سن گها از نوع تولئیتی و کالکآلکالن بوده و شاخص اشباع از آلومین این سنگها متاآلومین است. دیوریتها و گابروهاي برنورد از نوع پتاسیم متوسط بوده و از غنیشدگی نشان میدهند؛ در حالیکه عناصري Th بههمراه La, Rb, K, U, Pb لحاظ ویژگیهاي ژئوشیمیایی نسبت به عناصر ناسازگار تهیشدگی شاخصی را در مقایسه با کندریت ارائه میدهند. Nb, Ti, Ta, Sr, Ba مانند 0 بهدست آمده است. مقدار عددي نسبت / 0 تا 51214 / 143 ) دیوریتها و گابروهاي برنورد در گستره 51203 Nd/144Nd)i Sr)i 86 Sr/ 87 دیوریتها و گابروهاي ƐNd(T= 0 اندازهگیري شده است. مقدار عددي ( 552 / 0 تا 7135 / ) این تودههاي نفوذي در گستره 7038 Ɛ0Nd(present) 87 ) نمونههاي دیوریت و گابروهاي منطقه برنورد و مقادیر Sr/86Sr)i 4 بهدست آمده است. مقادیر پایین / 2 تا 0 / برنورد از 0 4 محاسبهشده است، نشاندهنده آن است که تولید چنین تودههاي نفوذي م یتواند به منبعی از گوشته / 0- تا 0 / این تودههاي نفوذي که 2 بالایی یا پوسته قارهاي زیرین تحت آلایش قرارگرفته شده، نسبتداده شود. محیط تشکیل این دسته از سن گهاي کمپلک س پلوتونیک برنورد، حاشیه فعال قاره و محیط کمان آتشفشانی 1 است که میتواند به فرورانش پوسته اقیانوسی موجود ب ین خرد قاره ایران مرکزي و بلوك افغان مرتبط باشد. واژههاي کلیدي: کمپلکس، سنسنجی، خرد قاره، ماگماتیسم، پرکامبرین، بردسکن، تکناpublishe

Quantifying Non-Photosynthetic Vegetation in a Mixed Grassland Using Hyperspectral Data: A Case Study in Kenya

This study is a first attempt to quantify the non-photosynthetic vegetation (NPV) fraction at a semiarid grassland site located in Kenya. We have first applied a model already developed and calibrated for crop analysis to predict grassland NPV from field spectral reflectance data. The second step will be to refine the model and apply it to the PRISMA image to obtain a quantitative map