arXiv subjects

D. Ortega

Publications and source records attributed to D. Ortega.

5 recordsLinked to original sources

arXiv2025

Bridging the divide: Economic exchange and segregation in dual-income cities

Segregation is a growing concern around the world. One of its main manifestations is the creation of ghettos, whose inhabitants have difficult access to well-paid jobs, which are often located far from their homes. In order to study this phenomenon, we propose an extension of Schelling's model of segregation to take into account the existence of economic exchanges. To approximate a geographical model of the city, we consider a small-world network with a defined real estate market. The evolution of the system has also been studied, finding that economic exchanges follow exponential laws and relocations are approximated by power laws. In addition to this, we consider the existence of delays in the actions of the agents, which mainly affect the happiness of those with fewer economic resources. Besides, the size of the economic exchange plays a crucial role in overall segregation. Despite its simplicity, we find that our model reproduces real-world situations such as the separation between favoured and handicapped economic areas, the importance of economic contacts between them to improve the distribution of wealth, and the existence of efficient and cheap transport to break the poverty cycles typical of disadvantaged zones.

physics.soc-ph↗

arXiv2012

Magneto-optic Faraday effect in maghemite nanoparticles/silica matrix nanocomposites prepared by the Sol-Gel method

Bulk monolithic samples of γ-Fe2O3/SiO2 composites with different iron oxide/silica ratios have been prepared by the sol-gel technique. Iron oxide nanoparticles are obtained in-situ during heat treatment of samples and silica matrix consolidation. Preparation method was previously optimized to minimize the percentage of antiferromagnetic α-Fe2O3 and parallelepipeds of roughly 2x5x12 mm3, with good mechanical stability, are obtained. RT magnetization curves show a non-hysteretic behavior. Thus, magnetization measurements have been well fitted to an expression that combines the Langevin equation with an additional linear term, indicating that some of the nanoparticles are still superparamagnetic as confirmed by X-ray diffraction and electron microscopy measurements. Zero field cooled /field cooled experiments show curves with slightly different shapes, depending on the size and shape distribution of nanoparticles for a given composition. Magneto-optical Faraday effect measurements show that the Faraday rotation is proportional to magnetization of the samples, as expected. As a demonstration of their sensing possibilities, the relative intensity of polarized light, measured at 5° from the extinction angle, was plotted versus applied magnetic field.

cond-mat.mtrl-sci↗

arXiv2007

Hodge polynomials of the moduli spaces of triples of rank (2,2)

Let $X$ be a smooth projective curve of genus $g\geq 2$ over the complex numbers. A holomorphic triple $(E_1,E_2,ϕ)$ on $X$ consists of two holomorphic vector bundles $E_{1}$ and $E_{2}$ over $X$ and a holomorphic map $ϕ\colon E_{2} \to E_{1}$. There is a concept of stability for triples which depends on a real parameter $σ$. In this paper, we determine the Hodge polynomials of the moduli spaces of $σ$-stable triples with $\mathrm{rk}(E_1)=\mathrm{rk}(E_2)=2$, using the theory of mixed Hodge structures (in the cases that they are smooth and compact). This gives in particular the Poincar{é} polynomials of these moduli spaces. As a byproduct, we also give the Hodge polynomial of the moduli space of even degree rank 2 stable vector bundles.

math.AG↗

arXiv2006

Hodge polynomials of the moduli spaces of pairs

Let $X$ be a smooth projective curve of genus $g\geq 2$ over the complex numbers. A holomorphic pair on $X$ is a couple $(E,ϕ)$, where $E$ is a holomorphic bundle over $X$ of rank $n$ and degree $d$, and $ϕ\in H^0(E)$ is a holomorphic section. In this paper, we determine the Hodge polynomials of the moduli spaces of rank 2 pairs, using the theory of mixed Hodge structures. We also deal with the case in which $E$ has fixed determinant.

math.AG↗

arXiv2006

Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb

We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity.

physics.atom-ph↗