185 research outputs found
Block freeze-concentration of coffee extract: Effect of freezing and thawing stages on solute recovery and bioactive compounds
Coffee extract was freeze-concentrated using the total block technique. The effects of four parameters
were evaluated: the initial coffee mass fraction (5 and 15% w/w), the cooling temperature ( 10 and
20 C), the heating temperature (20 and 40 C) and the freezing direction (parallel and counter-flow
to the thawing direction). The solid concentration was measured during the thawing stage to quantify
the solute recovery and the concentration index for one stage of freeze concentration. The coffee mass
fraction, the freezing direction and the cooling temperature significantly influenced the solute recovery.
A concentration index between 1 and 2.3 was obtained in one cycle. The effect of block freeze concentration
on the bioactive compound concentration and the antioxidant activity was measured. The coffee bioactive
compounds were distributed in proportion to the total solid content in the ice and liquid.
Therefore, block freeze concentration is an effective technique to preserve functional properties of coffee
extracts.Postprint (published version
Spectral and Energy Efficiency Maximization of MISO STAR-RIS-assisted URLLC Systems
This paper proposes a general optimization framework to improve the spectral
and energy efficiency (EE) of ultra-reliable low-latency communication (URLLC)
simultaneous-transfer-and-receive (STAR) reconfigurable intelligent surface
(RIS)-assisted interference-limited systems with finite block length (FBL).
This framework can solve a large variety of optimization problems in which the
objective and/or constraints are linear functions of the rates and/or EE of
users. Additionally, the framework can be applied to any interference-limited
system with treating interference as noise as the decoding strategy at
receivers. We consider a multi-cell broadcast channel as an example and show
how this framework can be specialized to solve the minimum-weighted rate,
weighted sum rate, global EE and weighted EE of the system. We make realistic
assumptions regarding the (STAR-)RIS by considering three different feasibility
sets for the components of either regular RIS or STAR-RIS. Our results show
that RIS can substantially increase the spectral and EE of URLLC systems if the
reflecting coefficients are properly optimized. Moreover, we consider three
different transmission strategies for STAR-RIS as energy splitting (ES), mode
switching (MS), and time switching (TS). We show that STAR-RIS can outperform a
regular RIS when the regular RIS cannot cover all the users. Furthermore, it is
shown that the ES scheme outperforms the MS and TS schemes.Comment: Accepted at IEEE ACCES
Energy-efficient Rate Splitting for MIMO STAR-RIS-assisted Broadcast Channels with I/Q Imbalance
This paper proposes an energy-efficient scheme for multicell multiple-input,
multiple-output (MIMO) simultaneous transmit and reflect (STAR) reconfigurable
intelligent surfaces (RIS)-assisted broadcast channels by employing rate
splitting (RS) and improper Gaussian signaling (IGS). Regular RISs can only
reflect signals. Thus, a regular RIS can assist only when the transmitter and
receiver are in the reflection space of the RIS. However, a STAR-RIS can
simultaneously transmit and reflect, thus providing a 360-degrees coverage. In
this paper, we assume that transceivers may suffer from I/Q imbalance (IQI). To
compensate for IQI, we employ IGS. Moreover, we employ RS to manage intracell
interference. We show that RIS can significantly improve the energy efficiency
(EE) of the system when RIS components are carefully optimized. Additionally,
we show that STAR-RIS can significantly outperform a regular RIS when the
regular RIS cannot cover all the users. We also show that RS can highly
increase the EE comparing to treating interference as noise.Comment: Accepted at the 31st European Signal Processing Conference (EUSIPCO
2023
SNR Maximization in Beyond Diagonal RIS-assisted Single and Multiple Antenna Links
Reconfigurable intelligent surface (RIS) architectures not limited to
diagonal phase shift matrices have recently been considered to increase their
flexibility in shaping the wireless channel. One of these beyond-diagonal RIS
or BD-RIS architectures leads to a unitary and symmetric RIS matrix. In this
letter, we consider the problem of maximizing the signal-to-noise ratio (SNR)
in single and multiple antenna links assisted by a BD-RIS. The Max-SNR problem
admits a closed-form solution based on the Takagi factorization of a certain
complex and symmetric matrix. This allows us to solve the max-SNR problem for
SISO, SIMO, and MISO channels.Comment: 5 pages, 2 figure
Optimization of Rate-Splitting Multiple Access in Beyond Diagonal RIS-assisted URLLC Systems
This paper proposes a general optimization framework for rate splitting
multiple access (RSMA) in beyond diagonal (BD) reconfigurable intelligent
surface (RIS) assisted ultra-reliable low-latency communications (URLLC)
systems. This framework can solve a large family of optimization problems in
which the objective and/or constraints are linear functions of the rates and/or
energy efficiency (EE) of users. Using this framework, we show that RSMA and
RIS can be mutually beneficial tools when the system is overloaded, i.e., when
the number of users per cell is higher than the number of base station (BS)
antennas. Additionally, we show that the benefits of RSMA increase when the
packets are shorter and/or the reliability constraint is more stringent.
Furthermore, we show that the RSMA benefits increase with the number of users
per cell and decrease with the number of BS antennas. Finally, we show that RIS
(either diagonal or BD) can highly improve the system performance, and BD-RIS
outperforms regular RIS.Comment: submitted to at IEEE journa
Ice morphology modification and solute recovery improvement by heating and annealing during block freeze-concentration of coffee extracts
Several treatments on ice blocks can be applied during block freeze-concentration to increase the solute recovery from the ice. In the present study, the changes in the ice block’s temperature and the application of annealing during the block freeze-concentration of aqueous coffee extracts were studied. The ice block was subjected to heating and annealing prior to the thawing stage. The effect of coolant temperature during ice block heating (T = -10 and -5 °C) and the application of annealing (+, -) on solute recovery and ice structure morphology was evaluated. The use of annealing during block freeze-concentration modified the ice crystal morphology and increased the solute recovery only when it is applied at the highest temperature. In general, the annealing process increased the size and circularity of the ice crystals, consequently improving the solute recovery. Thus, annealing can be used to increase the solute recovery during block freeze-concentration.Postprint (published version
El optimizador de bucles del compilador Open64/ORC (parte 2)
Open64 y ORC (Open Research Compiler) son dos iniciativas de código abierto basadas en el compilador SGI Pro64. Open64 está gestionada por miembros de la Universidad de Delaware, y ORC es una extensión del compilador desarrollada por Intel y la Chinese Academy of Science. Para más información consultar las respectivas páginas web [2] y [1].
SGI Pro64 es un conjunto de compiladores optimizadores desarrollados por SGI. Incluye compiladores de C, C++ y Fortran90/95 que siguen los estándares ABI y API de Linux IA-64. Los archivos fuente son de dominio público y se distribuyen bajo los términos de la GNU General Public License. El conjunto
de compiladores está disponible para correr sobre plataformas Linux IA-32 e IA-64.
Este documento continúa el trabajo iniciado en los technical reports “Introducción al compilador Open64/ORC” [10] y “El optimizador de bucles del compilador Open64/ORC (parte 1)” [11]. El primero describe los componentes del compilador y la representación intermedia que se utiliza como interficie común entre ellos. El segundo documento se centra específicamente en uno de los componentes del compilador: el optimizador de bucles.Postprint (published version
Effect of process parameters on progressive freeze concentration of sucrose solutions
The progressive freeze concentration of sucrose solutions was tested. The effect of the initial concentration of the solution (C0), the temperature of the refrigerant (T) and the stirring speed (¿) on the final concentration of the solution was determined. The effects were significant on the freeze concentration, for both individual and combined effects. The maximum concentration achieved in the progressive freeze concentration was 53º Brix, when the initial concentration was 35º Brix, at a speed of 800 rpm and a temperature of refrigerant of -20°C. The best values of the concentration index are obtained at low concentrations, high stirring speed and low temperature. The average distribution coefficient increased with the initial concentration of the solution. The average yield parameter at different initial concentrations is around 0.6 kg ice·kg sol-1·h-1.Postprint (author's final draft
Freeze desalination by the integration of falling film and block freeze concentration techniques
Block and falling film freeze concentration are two technologies that separate water by freezing,with the
potential to desalinate seawater. In this study, the
integration of two freeze concentration techniques as
an alternative to obtain potable water was analysed.
Water with 0.5%–8% NaCl was freeze-concentrated by
the falling film technique. The ice from each stage was fractionally thawed to recover the solids retained inPostprint (updated version
Dynamic flight plan design for UAS remote sensing applications
The development of Flight Control Systems (FCS) coupled with the availability of other
Commercial Off-The Shelf (COTS) components is enabling the introduction of Unmanned
Aircraft Systems (UAS) into the civil market. UAS have great potential to be used in a
wide variety of civil applications such as environmental applications, emergency situations,
surveillance tasks and more. In general, they are specially well suited for the so-called
D-cube operations (Dirty, Dull or Dangerous).
Current technology greatly facilitates the construction of UAS. Sophisticated flight con-
trol systems also make them accessible to end users with little aeronautical expertise. How-
ever, we believe that for its successful introduction into the civil market, progress needs
to be made to deliver systems able to perform a wide variety of missions with minimal
reconfiguration and with reduced operational costs.
Most current flight plan specification mechanisms consist in a simple list of waypoints, an
approach that has important limitations. This paper proposes a new specification mech-
anism with semantically richer constructs that will enable the end user to specify more
complex flight plans. The proposed formalism provides means for specifying iterative be-
havior, conditional branching and other constructs to dynamically adapt the flight path to
mission circumstances. Collaborating with the FCS, a new module on-board the UAS will
be in charge of executing these plans.
This research also studies how the proposed flight plan structure can be tailored to the
specific needs of remote sensing. For these type of applications well structured and efficient
area and perimeter scanning is mandatory. In this paper we introduce several strategies
focused to optimize the scanning process for tactical or mini UAS. The paper also presents
a prototype implementation of this module and the results obtained in simulations.Postprint (published version
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